1
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Goodwin MJ, Dickenson JC, Ripak A, Deetz AM, McCarthy JS, Meyer GJ, Troian-Gautier L. Factors that Impact Photochemical Cage Escape Yields. Chem Rev 2024; 124:7379-7464. [PMID: 38743869 DOI: 10.1021/acs.chemrev.3c00930] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 05/16/2024]
Abstract
The utilization of visible light to mediate chemical reactions in fluid solutions has applications that range from solar fuel production to medicine and organic synthesis. These reactions are typically initiated by electron transfer between a photoexcited dye molecule (a photosensitizer) and a redox-active quencher to yield radical pairs that are intimately associated within a solvent cage. Many of these radicals undergo rapid thermodynamically favored "geminate" recombination and do not diffuse out of the solvent cage that surrounds them. Those that do escape the cage are useful reagents that may undergo subsequent reactions important to the above-mentioned applications. The cage escape process and the factors that determine the yields remain poorly understood despite decades of research motivated by their practical and fundamental importance. Herein, state-of-the-art research on light-induced electron transfer and cage escape that has appeared since the seminal 1972 review by J. P. Lorand entitled "The Cage Effect" is reviewed. This review also provides some background for those new to the field and discusses the cage escape process of both homolytic bond photodissociation and bimolecular light induced electron transfer reactions. The review concludes with some key goals and directions for future research that promise to elevate this very vibrant field to even greater heights.
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Affiliation(s)
- Matthew J Goodwin
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - John C Dickenson
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Alexia Ripak
- Université catholique de Louvain (UCLouvain), Institut de la Matière Condensée et des Nanosciences (IMCN), Molecular Chemistry, Materials and Catalysis (MOST), Place Louis Pasteur 1, bte L4.01.02, 1348 Louvain-la-Neuve, Belgium
| | - Alexander M Deetz
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Jackson S McCarthy
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Gerald J Meyer
- Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
| | - Ludovic Troian-Gautier
- Université catholique de Louvain (UCLouvain), Institut de la Matière Condensée et des Nanosciences (IMCN), Molecular Chemistry, Materials and Catalysis (MOST), Place Louis Pasteur 1, bte L4.01.02, 1348 Louvain-la-Neuve, Belgium
- Wel Research Institute, Avenue Pasteur 6, 1300 Wavre, Belgium
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2
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Marques HM. The inorganic chemistry of the cobalt corrinoids - an update. J Inorg Biochem 2023; 242:112154. [PMID: 36871417 DOI: 10.1016/j.jinorgbio.2023.112154] [Citation(s) in RCA: 8] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2023] [Revised: 01/23/2023] [Accepted: 01/26/2023] [Indexed: 02/05/2023]
Abstract
The inorganic chemistry of the cobalt corrinoids, derivatives of vitamin B12, is reviewed, with particular emphasis on equilibrium constants for, and kinetics of, their axial ligand substitution reactions. The role the corrin ligand plays in controlling and modifying the properties of the metal ion is emphasised. Other aspects of the chemistry of these compounds, including their structure, corrinoid complexes with metals other than cobalt, the redox chemistry of the cobalt corrinoids and their chemical redox reactions, and their photochemistry are discussed. Their role as catalysts in non-biological reactions and aspects of their organometallic chemistry are briefly mentioned. Particular mention is made of the role that computational methods - and especially DFT calculations - have played in developing our understanding of the inorganic chemistry of these compounds. A brief overview of the biological chemistry of the B12-dependent enzymes is also given for the reader's convenience.
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Affiliation(s)
- Helder M Marques
- Molecular Sciences Institute, School of Chemistry, University of the Witwatersrand, Johannesburg 2050, South Africa.
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3
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Welfare JG, Mortelliti MJ, McGlade CA, Hartman TW, Dempsey JL, Lawrence DS. Assessment of Photoreleasable Linkers and Light-Capturing Antennas on a Photoresponsive Cobalamin Scaffold. J Org Chem 2022; 87:5076-5084. [PMID: 35353509 PMCID: PMC9727707 DOI: 10.1021/acs.joc.1c02931] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Cobalamin has shown promise as a light-sensitive drug delivery platform owing to its ease of modification and the high quantum yields for drug photorelease. However, studies to date on the general photochemistry of alkyl cobalamins have primarily focused on methyl and adenosyl-substituted derivatives, the natural cofactors present in various enzymatic species. We describe the synthesis and photolytic behavior of cobalamin conjugates comprised of different combinations of fluorophores and β-axial ligands. In general, cobalamin conjugates containing β-axial alkyl substituents undergo efficient photolysis under aqueous conditions, with quantum yields up to >40%. However, substituents that are large and hydrophobic, or unable to readily support the presumed radical intermediate, suffer less efficient photolysis (<15%) than smaller, water-soluble, analogs. By contrast, quantum yields improve by 2-fold in DMF for cobalamins containing large hydrophobic β-axial substituents. This suggests that drug release from carriers comprised of membranous compartments, such as liposomes, may be significantly more efficient than the corresponding photorelease in an aqueous environment. Finally, we explored the impact of fluorophores on the photolysis of alkyl cobalamins under tissue-mimetic conditions. Cobalamins substituted with efficient photon-capturing fluorophores display up to 4-fold enhancements in photolysis relative to unsubstituted derivatives. In summary, we have shown that the photosensitivity of alkyl cobalamin conjugates can be tuned by altering the Co-appended alkyl moiety, modulating the polarity of the environment (solvent), and installing photon-capturing fluorophores onto the cobalamin framework.
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4
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Ghosh AP, Lodowski P, Kozlowski PM. Aerobic photolysis of methylcobalamin: unraveling the photoreaction mechanism. Phys Chem Chem Phys 2022; 24:6093-6106. [PMID: 35212341 DOI: 10.1039/d1cp02013g] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The photo-reactivity of cobalamins (Cbls) is influenced by the nature of axial ligands and the cofactor's environment. While the biologically active forms of Cbls with alkyl axial ligands, such as methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl), are considered to be photolytically active, in contrast, the non-alkyl Cbls are photostable. In addition to these, the photolytic properties of Cbls can also be modulated in the presence of molecular oxygen, i.e., under aerobic conditions. Herein, the photoreaction of the MeCbl in the presence of oxygen has been explored using density functional theory (DFT) and time-dependent DFT (TD-DFT). The first stage of the aerobic photoreaction is the activation of the Co-C bond and the formation of the ligand field (LF) electronic state through the displacement of axial bonds. Once the photoreaction reaches the LF excited state, three processes can occur: namely the formation of OO-CH3 through the reaction of CH3 with molecular oxygen, de-activation of the {Im⋯[CoII(corrin)]⋯CH3}+ sub-system from the LF electronic state by changing the electronic configuration from (dyz)1(dz2)2 to (dyz)2(dz2)1 and the formation of the deactivation complex (DC) complex via the recombination of OO-CH3 species with the de-excited [CoII(corrin)] system. In the proposed mechanism, the deactivation of the [CoII(corrin)] subsystem may coexist with the formation of OO-CH3, followed by immediate relaxation of the subsystems in the ground state. Moreover, the formation of the OO-CH3 species followed by the formation of the {[CoIII(corrin)]-OO-CH3}+ complex stabilizes the system compared to the reactant complex.
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Affiliation(s)
- Arghya Pratim Ghosh
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA.
| | - Piotr Lodowski
- Institute of Chemistry, University of Silesia in Katowice, Szkolna 9, PL-40 006 Katowice, Poland
| | - Pawel M Kozlowski
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA.
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5
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Yoon H, Park S, Lim M. Photodissociation Dynamics of Nitric Oxide from N-Acetylcysteine- or N-Acetylpenicillamine-bound Roussin's Red Ester. ACS OMEGA 2021; 6:27158-27169. [PMID: 34693136 PMCID: PMC8529681 DOI: 10.1021/acsomega.1c03820] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Accepted: 09/29/2021] [Indexed: 05/05/2023]
Abstract
The photochemical release of nitric oxide (NO) from a NO precursor is advantageous in terms of spatial, temporal, and dosage control of NO delivery to target sites. To realize full control of the quantitative NO administration from photoactivated NO precursors, it is necessary to have detailed dynamical information on the photodissociation of NO from NO precursors. We synthesized two new water-soluble Roussin's red esters (RREs), [Fe2(μ-N-acetylcysteine)2(NO)4] and [Fe2(μ-N-acetylpenicillamine)2(NO)4], which have five times longer lifetime than the well-known [Fe2(μ-cysteine)2(NO)4]. The photodissociation dynamics of NO from these RREs in water were investigated over a broad time range from 0.3 ps to 10 μs after excitation at 310 and 400 nm using femtosecond time-resolved infrared (IR) spectroscopy. When these RREs are excited, they either release one NO, producing a radical species deficient in one NO (R), [Fe2(μ-RS)2(NO)3], or relax into the ground state without photodeligation via an electronically excited intermediate state (M). R appears immediately after photoexcitation, suggesting that one NO is photodissociated faster than 0.3 ps. A certain fraction of R undergoes geminate recombination (GR) with NO with a time constant of 7-9 ps, while the remaining R competitively binds to the solvent. Solvent-bound R eventually bimolecularly recombines with NO with a rate constant of (1.3-1.6) × 108 M-1 s-1. For a given RRE molecule, the fractional yield of M (0.62-0.76) depends on the excitation wavelength (λex); however, the relaxation time of M (6 ± 1 ns) is independent of λex. Although the primary quantum yield of NO photodissociation (Φ1) was found to be 0.24-0.38, the final yield of NO suitable for other reactions (Φ2) was reduced to 0.14-0.29 due to the picosecond GR of the dissociated NO with R. Detailed photoexcitation dynamics of RRE can be utilized in the quantitative control of NO administration at a specific site and time, promoting pin-point usage of NO in chemistry and biology. We demonstrate that femtosecond IR spectroscopy combined with quantum chemical calculations is a powerful method for obtaining detailed dynamic information on photoactivated NO precursors such as Φ1 and Φ2, the GR yield, and secondary reactions of the nascent photoproducts, which are essential information for the design of efficient photoactivated NO precursors and their quantitative utilization.
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6
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Weinstain R, Slanina T, Kand D, Klán P. Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials. Chem Rev 2020; 120:13135-13272. [PMID: 33125209 PMCID: PMC7833475 DOI: 10.1021/acs.chemrev.0c00663] [Citation(s) in RCA: 253] [Impact Index Per Article: 63.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2020] [Indexed: 02/08/2023]
Abstract
Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.
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Affiliation(s)
- Roy Weinstain
- School
of Plant Sciences and Food Security, Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 6997801, Israel
| | - Tomáš Slanina
- Institute
of Organic Chemistry and Biochemistry of the Czech Academy of Sciences, Flemingovo nám. 2, 166 10 Prague, Czech Republic
| | - Dnyaneshwar Kand
- School
of Plant Sciences and Food Security, Faculty of Life Sciences, Tel-Aviv University, Tel-Aviv 6997801, Israel
| | - Petr Klán
- Department
of Chemistry and RECETOX, Faculty of Science, Masaryk University, Kamenice 5, 625 00 Brno, Czech Republic
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7
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Ghosh AP, Lodowski P, Bazarganpour A, Leks M, Kozlowski PM. Aerobic photolysis of methylcobalamin: structural and electronic properties of the Cbl-O-O-CH 3 intermediate. Dalton Trans 2020; 49:4114-4124. [PMID: 32142090 DOI: 10.1039/c9dt03740c] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Photolysis of methylcobalamin (MeCbl) in the presence of molecular oxygen (O2) has been investigated using density functional theory (DFT) and time-dependent DFT (TD-DFT). The key step involves the formation of the Cbl-O-O-CH3 intermediate as a result of triplet O2 insertion in the Co-C bond in the presence of light. Analysis of low-lying excited states shows that the presence of light is only needed to activate the Co-C bond via the formation of the ligand field (LF) state. The insertion of O2, as well as the change in the spin state, takes place in the ground state. The analysis of the structural and electronic properties of the Cbl-O-O-CH3 intermediate is presented and possible decomposition also discussed.
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Affiliation(s)
- Arghya Pratim Ghosh
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA.
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8
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Toda MJ, Lodowski P, Mamun AA, Jaworska M, Kozlowski PM. Photolytic properties of the biologically active forms of vitamin B12. Coord Chem Rev 2019. [DOI: 10.1016/j.ccr.2018.12.017] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
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9
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Mamun AA, Toda MJ, Lodowski P, Kozlowski PM. Photolytic Cleavage of Co–C Bond in Coenzyme B12-Dependent Glutamate Mutase. J Phys Chem B 2019; 123:2585-2598. [DOI: 10.1021/acs.jpcb.8b07547] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Abdullah Al Mamun
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Megan J. Toda
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Piotr Lodowski
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia in Katowice, Szkolna 9, PL-40 006 Katowice, Poland
| | - Pawel M. Kozlowski
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
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10
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Mamun AA, Toda MJ, Kozlowski PM. Can photolysis of the Co C bond in coenzyme B12-dependent enzymes be used to mimic the native reaction? JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2019; 191:175-184. [DOI: 10.1016/j.jphotobiol.2018.12.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2018] [Revised: 12/19/2018] [Accepted: 12/20/2018] [Indexed: 12/22/2022]
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11
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Ghosh AP, Mamun AA, Kozlowski PM. How does the mutation in the cap domain of methylcobalamin-dependent methionine synthase influence the photoactivation of the Co–C bond? Phys Chem Chem Phys 2019; 21:20628-20640. [DOI: 10.1039/c9cp01849b] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The topology of the S1 PES is modulated by introducing a mutation at the F708 position. The mutation influences the photoactivation of the Co–C bond by decreasing the rate of geminate recombination and altering the rate of radical pair formation.
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12
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Ghosh AP, Mamun AA, Lodowski P, Jaworska M, Kozlowski PM. Mechanism of the photo-induced activation of Co C bond in methylcobalamin-dependent methionine synthase. JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY B-BIOLOGY 2018; 189:306-317. [DOI: 10.1016/j.jphotobiol.2018.09.015] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/10/2018] [Revised: 09/12/2018] [Accepted: 09/18/2018] [Indexed: 11/26/2022]
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13
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Mamun AA, Toda MJ, Lodowski P, Jaworska M, Kozlowski PM. Mechanism of Light Induced Radical Pair Formation in Coenzyme B12-Dependent Ethanolamine Ammonia-Lyase. ACS Catal 2018. [DOI: 10.1021/acscatal.8b00120] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- Abdullah Al Mamun
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Megan J. Toda
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Piotr Lodowski
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia in Katowice, Szkolna 9, PL-40 006 Katowice, Poland
| | - Maria Jaworska
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia in Katowice, Szkolna 9, PL-40 006 Katowice, Poland
| | - Pawel M. Kozlowski
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
- Department of Food Sciences, Medical University of Gdansk, Al. Gen. J. Hallera 107, 80-416 Gdansk, Poland
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14
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Abstract
This Perspective provides the first detailed overview of the photoresponse of vitamin B12 and its derivatives, from the early, photophysical events to the burgeoning area of B12-dependent photobiology.
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Affiliation(s)
- Alex R. Jones
- School of Chemistry
- Photon Science Institute and Manchester Institute of Biotechnology
- The University of Manchester
- Manchester
- UK
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15
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Garabato BD, Lodowski P, Jaworska M, Kozlowski PM. Mechanism of Co-C photodissociation in adenosylcobalamin. Phys Chem Chem Phys 2016; 18:19070-82. [PMID: 27356617 DOI: 10.1039/c6cp02136k] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
A mechanism of Co-C bond photodissociation in the base-on form of adenosylcobalamin (AdoCbl) was investigated by time-dependent density functional theory (TD-DFT). The key mechanistic step involves singlet radical pair (RP) generation from the first electronically excited state (S1). To connect TD-DFT calculations with ultra-fast excited state dynamics, the potential energy surface (PES) of the S1 state was constructed using Co-C and Co-NIm axial coordinates. The S1 PES can be characterized by two minima separated by a seam resulting from the crossing of two surfaces, of metal-to-ligand charge transfer (MLCT) character near the minimum, and a shallow ligand field (LF) surface at elongated axial bond distances. Only one possible pathway for photolysis (path A) was identified based on energetic grounds. This pathway is characterized by the first elongation of the Co-C bond, followed by photolysis from an LF state where the axial base is partially detached. A new perspective on the photolysis of AdoCbl is then gained by connecting TD-DFT results with available experimental observations.
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Affiliation(s)
- Brady D Garabato
- Department of Chemistry, University of Louisville, 2320 South Brook Street, Louisville, Kentucky 40202, USA.
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16
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Kozlowski PM, Garabato BD, Lodowski P, Jaworska M. Photolytic properties of cobalamins: a theoretical perspective. Dalton Trans 2016; 45:4457-70. [PMID: 26865262 DOI: 10.1039/c5dt04286k] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
This Perspective Article highlights recent theoretical developments, and summarizes the current understanding of the photolytic properties of cobalamins from a computational point of view. The primary focus is on two alkyl cobalamins, methylcobalamin (MeCbl) and adenosylcobalamin (AdoCbl), as well as two non-alkyl cobalamins, cyanocobalamin (CNCbl) and hydroxocobalamin (HOCbl). Photolysis of alkyl cobalamins involves low-lying singlet excited states where photodissociation of the Co-C bond leads to formation of singlet-born alkyl/cob(ii)alamin radical pairs (RPs). Potential energy surfaces (PESs) associated with cobalamin low-lying excited states as functions of both axial bonds, provide the most reliable tool for initial analysis of their photochemical and photophysical properties. Due to the complexity, and size limitations associated with the cobalamins, the primary method for calculating ground state properties is density functional theory (DFT), while time-dependent DFT (TD-DFT) is used for electronically excited states. For alkyl cobalamins, energy pathways on the lowest singlet surface, connecting metal-to-ligand charge transfer (MLCT) and ligand field (LF) minima, can be associated with photo-homolysis of the Co-C bond observed experimentally. Additionally, energy pathways between minima and seams associated with crossing of S1/S0 surfaces, are the most efficient for internal conversion (IC) to the ground state. Depending on the specific cobalamin, such IC may involve simultaneous elongation of both axial bonds (CNCbl), or detachment of axial base followed by corrin ring distortion (MeCbl). The possibility of intersystem crossing, and the formation of triplet RPs is also discussed based on Landau-Zener theory.
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Affiliation(s)
- Pawel M Kozlowski
- Department of Chemistry, University of Louisville, Louisville, Kentucky 40292, USA.
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17
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Garabato BD, Kumar N, Lodowski P, Jaworska M, Kozlowski PM. Electronically excited states of cob(ii)alamin: insights from CASSCF/XMCQDPT2 and TD-DFT calculations. Phys Chem Chem Phys 2016; 18:4513-26. [DOI: 10.1039/c5cp06439b] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
The low-lying excited states of cob(ii)alamin were investigated using time-dependent density functional theory (TD-DFT), and multiconfigurational CASSCF/XMCQDPT2 methodology, to help understand their role in B12-mediated reactions.
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Affiliation(s)
| | - Neeraj Kumar
- Department of Chemistry
- University of Louisville
- Louisville
- USA
- Pacific Northwest National Laboratory
| | - Piotr Lodowski
- Department of Theoretical Chemistry
- Institute of Chemistry
- University of Silesia
- PL-40 006 Katowice
- Poland
| | - Maria Jaworska
- Department of Theoretical Chemistry
- Institute of Chemistry
- University of Silesia
- PL-40 006 Katowice
- Poland
| | - Pawel M. Kozlowski
- Department of Chemistry
- University of Louisville
- Louisville
- USA
- Visiting Professor at the Department of Food Sciences
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18
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Lodowski P, Jaworska M, Garabato BD, Kozlowski PM. Mechanism of Co–C Bond Photolysis in Methylcobalamin: Influence of Axial Base. J Phys Chem A 2015; 119:3913-28. [DOI: 10.1021/jp5120674] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Piotr Lodowski
- Department
of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
| | - Maria Jaworska
- Department
of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
| | - Brady D. Garabato
- Department
of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Pawel M. Kozlowski
- Department
of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
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19
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Lodowski P, Jaworska M, Andruniów T, Garabato BD, Kozlowski PM. Mechanism of Co–C Bond Photolysis in the Base-On Form of Methylcobalamin. J Phys Chem A 2014; 118:11718-34. [DOI: 10.1021/jp508513p] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Piotr Lodowski
- Department
of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
| | - Maria Jaworska
- Department
of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland
| | - Tadeusz Andruniów
- Institute
of Physical and Theoretical Chemistry, Department of Chemistry, Wroclaw University of Technology, 50-370 Wroclaw, Poland
| | - Brady D. Garabato
- Department
of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
| | - Pawel M. Kozlowski
- Department
of Chemistry, University of Louisville, Louisville, Kentucky 40292, United States
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20
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Liu H, Kornobis K, Lodowski P, Jaworska M, Kozlowski PM. TD-DFT insight into photodissociation of the Co-C bond in coenzyme B12. Front Chem 2014; 1:41. [PMID: 24790969 PMCID: PMC3982521 DOI: 10.3389/fchem.2013.00041] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2013] [Accepted: 12/24/2013] [Indexed: 11/30/2022] Open
Abstract
Coenzyme B12 (AdoCbl) is one of the most biologically active forms of vitamin B12, and continues to be a topic of active research interest. The mechanism of Co-C bond cleavage in AdoCbl, and the corresponding enzymatic reactions are however, not well understood at the molecular level. In this work, time-dependent density functional theory (TD-DFT) has been applied to investigate the photodissociation of coenzyme B12. To reduce computational cost, while retaining the major spectroscopic features of AdoCbl, a truncated model based on ribosylcobalamin (RibCbl) was used to simulate Co-C photodissociation. Equilibrium geometries of RibCbl were obtained by optimization at the DFT/BP86/TZVP level of theory, and low-lying excited states were calculated by TD-DFT using the same functional and basis set. The calculated singlet states, and absorption spectra were simulated in both the gas phase, and water, using the polarizable continuum model (PCM). Both spectra were in reasonable agreement with experimental data, and potential energy curves based on vertical excitations were plotted to explore the nature of Co-C bond dissociation. It was found that a repulsive 3(σCo−C → σ*Co−C) triplet state became dissociative at large Co-C bond distance, similar to a previous observation for methylcobalamin (MeCbl). Furthermore, potential energy surfaces (PESs) obtained as a function of both Co-CRib and Co-NIm distances, identify the S1 state as a key intermediate generated during photoexcitation of RibCbl, attributed to a mixture of a metal-to-ligand charge transfer (MLCT) and a σ bonding-ligand charge transfer (SBLCT) states.
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Affiliation(s)
- Hui Liu
- Department of Chemistry, University of Louisville Louisville, KY, USA
| | - Karina Kornobis
- Department of Chemistry, University of Louisville Louisville, KY, USA
| | - Piotr Lodowski
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia Katowice, Poland
| | - Maria Jaworska
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia Katowice, Poland
| | - Pawel M Kozlowski
- Department of Chemistry, University of Louisville Louisville, KY, USA
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Photolytic cleavage of Co–C bond: A mechanistic study for the formation of solvent coordinated cobalt(II) complex. J Organomet Chem 2014. [DOI: 10.1016/j.jorganchem.2013.09.010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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Lodowski P, Jaworska M, Andruniów T, Garabato BD, Kozlowski PM. Mechanism of the S1 excited state internal conversion in vitamin B12. Phys Chem Chem Phys 2014; 16:18675-9. [DOI: 10.1039/c4cp02465f] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
To explain the photostability of vitamin B12, internal conversion of the S1 state was investigated using TD-DFT.
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Affiliation(s)
- Piotr Lodowski
- Department of Theoretical Chemistry
- Institute of Chemistry
- University of Silesia
- PL-40 006 Katowice, Poland
| | - Maria Jaworska
- Department of Theoretical Chemistry
- Institute of Chemistry
- University of Silesia
- PL-40 006 Katowice, Poland
| | - Tadeusz Andruniów
- Institute of Physical and Theoretical Chemistry
- Department of Chemistry
- Wroclaw University of Technology
- 50-370 Wroclaw, Poland
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Jones AR, Levy C, Hay S, Scrutton NS. Relating localized protein motions to the reaction coordinate in coenzyme B12-dependent enzymes. FEBS J 2013; 280:2997-3008. [DOI: 10.1111/febs.12223] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2013] [Revised: 02/27/2013] [Accepted: 02/27/2013] [Indexed: 01/27/2023]
Affiliation(s)
| | - Colin Levy
- Manchester Institute of Biotechnology and Faculty of Life Sciences; The University of Manchester; Manchester; UK
| | - Sam Hay
- Manchester Institute of Biotechnology and Faculty of Life Sciences; The University of Manchester; Manchester; UK
| | - Nigel S. Scrutton
- Manchester Institute of Biotechnology and Faculty of Life Sciences; The University of Manchester; Manchester; UK
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Jones AR, Russell HJ, Greetham GM, Towrie M, Hay S, Scrutton NS. Ultrafast infrared spectral fingerprints of vitamin B12 and related cobalamins. J Phys Chem A 2012; 116:5586-94. [PMID: 22612868 DOI: 10.1021/jp304594d] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Vitamin B(12) (cyanocobalamin, CNCbl) and its derivatives are structurally complex and functionally diverse biomolecules. The excited state and radical pair reaction dynamics that follow their photoexcitation have been previously studied in detail using UV-visible techniques. Similar time-resolved infrared (TRIR) data are limited, however. Herein we present TRIR difference spectra in the 1300-1700 cm(-1) region between 2 ps and 2 ns for adenosylcobalamin (AdoCbl), methylcobalamin (MeCbl), CNCbl, and hydroxocobalamin (OHCbl). The spectral profiles of all four cobalamins are complex, with broad similarities that suggest the vibrational excited states are related, but with a number of identifiable variations. The majority of the signals from AdoCbl and MeCbl decay with kinetics similar to those reported in the literature from UV-visible studies. However, there are regions of rapid (<10 ps) vibrational relaxation (peak shifts to higher frequencies from 1551, 1442, and 1337 cm(-1)) that are more pronounced in AdoCbl than in MeCbl. The AdoCbl data also exhibit more substantial changes in the amide I region and a number of more gradual peak shifts elsewhere (e.g., from 1549 to 1563 cm(-1)), which are not apparent in the MeCbl data. We attribute these differences to interactions between the bulky adenosyl and the corrin ring after photoexcitation and during radical pair recombination, respectively. Although spectrally similar to the initial excited state, the long-lived metal-to-ligand charge transfer state of MeCbl is clearly resolved in the kinetic analysis. The excited states of CNCbl and OHCbl relax to the ground state within 40 ps with few significant peak shifts, suggesting little or no homolysis of the bond between the Co and the upper axial ligand. Difference spectra from density functional theory calculations (where spectra from simplified cobalamins with an upper axial methyl were subtracted from those without) show qualitative agreement with the experimental data. They imply the excited state intermediates in the TRIR difference spectra resemble the dissociated states vibrationally (the cobalamin with the upper axial ligand missing) relative to the ground state with a methyl in this position. They also indicate that most of the TRIR signals arise from vibrations involving some degree of motion in the corrin ring. Such coupling of motions throughout the ring makes specific peak assignments neither trivial nor always meaningful, suggesting our data should be regarded as IR spectral fingerprints.
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Affiliation(s)
- Alex R Jones
- Manchester Interdisciplinary Biocentre and Faculty of Life Sciences, University of Manchester, UK
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Jones AR, Hardman SJO, Hay S, Scrutton NS. Is There a Dynamic Protein Contribution to the Substrate Trigger in Coenzyme B12-Dependent Ethanolamine Ammonia Lyase? Angew Chem Int Ed Engl 2011. [DOI: 10.1002/ange.201105132] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Jones AR, Hardman SJO, Hay S, Scrutton NS. Is there a dynamic protein contribution to the substrate trigger in coenzyme B12-dependent ethanolamine ammonia lyase? Angew Chem Int Ed Engl 2011; 50:10843-6. [PMID: 21948289 DOI: 10.1002/anie.201105132] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2011] [Indexed: 11/07/2022]
Affiliation(s)
- Alex R Jones
- Faculty of Life Sciences, Photon Science Institute and Manchester Interdisciplinary Biocentre, University of Manchester, Manchester M1 7DN, UK
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Robertson WD, Wang M, Warncke K. Characterization of protein contributions to cobalt-carbon bond cleavage catalysis in adenosylcobalamin-dependent ethanolamine ammonia-lyase by using photolysis in the ternary complex. J Am Chem Soc 2011; 133:6968-77. [PMID: 21491908 PMCID: PMC3092035 DOI: 10.1021/ja107052p] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Protein contributions to the substrate-triggered cleavage of the cobalt-carbon (Co-C) bond and formation of the cob(II)alamin-5'-deoxyadenosyl radical pair in the adenosylcobalamin (AdoCbl)-dependent ethanolamine ammonia-lyase (EAL) from Salmonella typhimurium have been studied by using pulsed-laser photolysis of AdoCbl in the EAL-AdoCbl-substrate ternary complex, and time-resolved probing of the photoproduct dynamics by using ultraviolet-visible absorption spectroscopy on the 10(-7)-10(-1) s time scale. Experiments were performed in a fluid dimethylsulfoxide/water cryosolvent system at 240 K, under conditions of kinetic competence for thermal cleavage of the Co-C bond in the ternary complex. The static ultraviolet-visible absorption spectra of holo-EAL and ternary complex are comparable, indicating that the binding of substrate does not labilize the cofactor cobalt-carbon (Co-C) bond by significantly distorting the equilibrium AdoCbl structure. Photolysis of AdoCbl in EAL at 240 K leads to cob(II)alamin-5'-deoxyadenosyl radical pair quantum yields of <0.01 at 10(-6) s in both holo-EAL and ternary complex. Three photoproduct states are populated following a saturating laser pulse, and labeled, P(f), P(s), and P(c). The relative amplitudes and first-order recombination rate constants of P(f) (0.4-0.6; 40-50 s(-1)), P(s) (0.3-0.4; 4 s(-1)), and P(c) (0.1-0.2; 0) are comparable in holo-EAL and in the ternary complex. Time-resolved, full-spectrum electron paramagnetic resonance (EPR) spectroscopy shows that visible irradiation alters neither the kinetics of thermal cob(II)alamin-substrate radical pair formation, nor the equilibrium between ternary complex and cob(II)alamin-substrate radical pair, at 246 K. The results indicate that substrate binding to holo-EAL does not "switch" the protein to a new structural state, which promptly stabilizes the cob(II)alamin-5'-deoxyadenosyl radical pair photoproduct, either through an increased barrier to recombination, a decreased barrier to further radical pair separation, or lowering of the radical pair state free energy, or a combination of these effects. Therefore, we conclude that such a change in protein structure, which is independent of changes in the AdoCbl structure, and specifically the Co-C bond length, is not a basis of Co-C bond cleavage catalysis. The results suggest that, following the substrate trigger, the protein interacts with the cofactor to contiguously guide the cleavage of the Co-C bond, at every step along the cleavage coordinate, starting from the equilibrium configuration of the ternary complex. The cleavage is thus represented by a diagonal trajectory across a free energy surface, that is defined by chemical (Co-C separation) and protein configuration coordinates.
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Affiliation(s)
| | - Miao Wang
- Department of Physics, Emory University, Atlanta, GA 30322
| | - Kurt Warncke
- Department of Physics, Emory University, Atlanta, GA 30322
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Jones AR, Woodward JR, Scrutton NS. Continuous wave photolysis magnetic field effect investigations with free and protein-bound alkylcobalamins. J Am Chem Soc 2010; 131:17246-53. [PMID: 19899795 DOI: 10.1021/ja9059238] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The activation of the Co-C bond in adenosylcobalamin-dependent enzymes generates a singlet-born Co(II)-adenosyl radical pair. Two of the salient questions regarding this process are: (1) What is the origin of the considerable homolysis rate enhancement achieved by this class of enzyme? (2) Are the reaction dynamics of the resultant radical pair sensitive to the application of external magnetic fields? Here, we present continuous wave photolysis magnetic field effect (MFE) data that reveal the ethanolamine ammonia lyase (EAL) active site to be an ideal microreactor in which to observe enhanced magnetic field sensitivity in the adenosylcobalamin radical pair. The observed field dependence is in excellent agreement with that calculated from published hyperfine couplings for the constituent radicals, and the magnitude of the MFE (<18%) is almost identical to that observed in a solvent containing 67% glycerol. Similar augmentation is not observed, however, in the equivalent experiments with EAL-bound methylcobalamin, where all field sensitivity observed in the free cofactor is washed out completely. Parallels are drawn between the latter case and the loss of field sensitivity in the EAL holoenzyme upon substrate binding (Jones et al. J. Am. Chem. Soc. 2007, 129, 15718-15727). Both are attributed to the rapid removal of the alkyl radical immediately after homolysis, such that there is inadequate radical pair recombination for the observation of field effects. Taken together, these results support the notion that rapid radical quenching, through the coupling of homolysis and hydrogen abstraction steps, and subsequent radical pair stabilization make a contribution to the observed rate acceleration of Co-C bond homolysis in adenosylcobalamin-dependent enzymes.
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Affiliation(s)
- Alex R Jones
- Manchester Interdisciplinary Biocentre and Faculty of Life Sciences, University of Manchester M1 7DN, United Kingdom
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Crean C, Geacintov NE, Shafirovich V. Methylation of 2'-deoxyguanosine by a free radical mechanism. J Phys Chem B 2009; 113:12773-81. [PMID: 19719172 PMCID: PMC2754879 DOI: 10.1021/jp903554n] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The mechanistic aspects of the methylation of guanine in DNA initiated by methyl radicals that are derived from the metabolic oxidation of some chemical carcinogens remain poorly understood. In this work, we investigated the kinetics and the formation of methylated guanine products by two methods: (i) the combination of *CH3 radicals and guanine neutral radicals, G(-H)*, and (ii) the direct addition of *CH3 radicals to guanine bases. The simultaneous generation of *CH3 and dG(-H)* radicals was triggered by the competitive one-electron oxidation of dimethyl sulfoxide (DMSO) and 2'-deoxyguanosine (dG) by photochemically generated sulfate radicals in deoxygenated aqueous buffer solutions (pH 7.5). The photolysis of methylcob(III)alamin to form *CH3 radicals was used to investigate the direct addition of these radicals to guanine bases. The major end products of the radical combination reactions are the 8-methyl-dG and N2-methyl-dG products formed in a ratio of 1:0.7. In contrast, the methylation of dG by *CH3 radicals generates mostly the 8-methyl-dG adduct and only minor quantities of N2-methyl-dG (1:0.13 ratio). The methylation of the self-complementary 5'-d(AACGCGAATTCGCGTT) duplexes was achieved by the selective oxidation of the guanines with carbonate radical anions in the presence of DMSO as the precursor of *CH3 radicals. The methyl-G lesions formed were excised by the enzymatic digestion and identified by LC-MS/MS methods using uniformly 15N-labeled 8-methyl-dG and N2-methyl-dG adducts as internal standards. The ratios of 8-methyl-G/N2-methyl-G lesions derived from the combination of methyl radicals with G(-H)* radicals positioned in double-stranded DNA or that with the free nucleoside dG(-H)* radicals were found to be similar. Utilizing the photochemical method and dipropyl or dibutyl sulfoxides as sources of alkyl radicals, the corresponding 8-alkyl-dG and N2-alkyl-dG adducts were also generated in ratios similar to those obtained with DMSO.
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Affiliation(s)
- Conor Crean
- Chemistry Department and Radiation and Solid State Laboratory, New York University, 31 Washington Place, New York, New York 10003-5180, USA
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30
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Lodowski P, Jaworska M, Andruniów T, Kumar M, Kozlowski PM. Photodissociation of Co−C Bond in Methyl- and Ethylcobalamin: An Insight from TD-DFT Calculations. J Phys Chem B 2009; 113:6898-909. [DOI: 10.1021/jp810223h] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Piotr Lodowski
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland; Institute of Physical and Theoretical Chemistry, Department of Chemistry, Wroclaw University of Technology, 50-370 Wroclaw, Poland; and Department of Chemistry, University of Louisville, Louisville, Kentucky 40292
| | - Maria Jaworska
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland; Institute of Physical and Theoretical Chemistry, Department of Chemistry, Wroclaw University of Technology, 50-370 Wroclaw, Poland; and Department of Chemistry, University of Louisville, Louisville, Kentucky 40292
| | - Tadeusz Andruniów
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland; Institute of Physical and Theoretical Chemistry, Department of Chemistry, Wroclaw University of Technology, 50-370 Wroclaw, Poland; and Department of Chemistry, University of Louisville, Louisville, Kentucky 40292
| | - Manoj Kumar
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland; Institute of Physical and Theoretical Chemistry, Department of Chemistry, Wroclaw University of Technology, 50-370 Wroclaw, Poland; and Department of Chemistry, University of Louisville, Louisville, Kentucky 40292
| | - Pawel M. Kozlowski
- Department of Theoretical Chemistry, Institute of Chemistry, University of Silesia, Szkolna 9, PL-40 006 Katowice, Poland; Institute of Physical and Theoretical Chemistry, Department of Chemistry, Wroclaw University of Technology, 50-370 Wroclaw, Poland; and Department of Chemistry, University of Louisville, Louisville, Kentucky 40292
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Robertson WD, Warncke K. Photolysis of adenosylcobalamin and radical pair recombination in ethanolamine ammonia-lyase probed on the micro- to millisecond time scale by using time-resolved optical absorption spectroscopy. Biochemistry 2009; 48:140-7. [PMID: 19072291 DOI: 10.1021/bi801659e] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The quantum yield and kinetics of decay of cob(II)alamin formed by pulsed-laser photolysis of adenosylcobalamin (AdoCbl; coenzyme B(12)) in AdoCbl-dependent ethanolamine ammonia-lyase (EAL) from Salmonella typhimurium have been studied on the 10(-7)-10(-1) s time scale at 295 K by using transient ultraviolet-visible absorption spectroscopy. The aim is to probe the mechanism of formation and stabilization of the cob(II)alamin-5'-deoxyadenosyl radical pair, which is a key intermediate in EAL catalysis, and the influence of substrate binding on this process. Substrate binding is required for cobalt-carbon bond cleavage in the native system. Photolysis of AdoCbl in EAL leads to a quantum yield at 10(-7) s for cob(II)alamin of 0.08 +/- 0.01, which is 3-fold smaller than for AdoCbl in aqueous solution (0.23 +/- 0.01). The protein binding site therefore suppresses photoproduct radical pair formation. Three photoproduct states, P(f), P(s), and P(c), are identified in holo-EAL by the different cob(II)alamin decay kinetics (subscripts denote fast, slow, and constant, respectively). These states have the following first-order decay rate constants and quantum yields: 2.2 x 10(3) s(-1) and 0.02 for P(f), 4.2 x 10(2) s(-1) and 0.01 for P(s), and constant amplitude, with no recombination, and 0.05 for P(c), respectively. Binding of the substrate analogue (S)-1-amino-2-propanol to EAL eliminates the P(f) state and lowers the quantum yield of P(c) (0.03) relative to that of P(s) (0.01) but does not significantly change the quantum yield or decay rate constant of P(s), relative to those of holo-EAL. The substrate analogue thus influences the quantum yield at 10(-7) s by changing the cage escape rate from the geminate cob(II)alamin-5'-deoxyadenosyl radical pair state. However, the predicted substrate analogue binding-induced increase in the quantum yield is not observed. It is proposed that the substrate analogue does not induce the radical pair stabilizing changes in the protein that are characteristic of true substrates.
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Reaction of the Co(II)-substrate radical pair catalytic intermediate in coenzyme B12-dependent ethanolamine ammonia-lyase in frozen aqueous solution from 190 to 217 K. Biophys J 2008; 95:5890-900. [PMID: 18805934 DOI: 10.1529/biophysj.108.138081] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The decay kinetics of the aminoethanol-generated Co(II)-substrate radical pair catalytic intermediate in ethanolamine ammonia-lyase from Salmonella typhimurium have been measured on timescales of <10(5) s in frozen aqueous solution from 190 to 217 K. X-band continuous-wave electron paramagnetic resonance (EPR) spectroscopy of the disordered samples has been used to continuously monitor the full radical pair EPR spectrum during progress of the decay after temperature step reaction initiation. The decay to a diamagnetic state is complete and no paramagnetic intermediate states are detected. The decay exhibits three kinetic regimes in the measured temperature range, as follows. i), Low temperature range, 190 < or = T < or = 207 K: the decay is biexponential with constant fast (0.57 +/- 0.04) and slow (0.43 +/- 0.04) phase amplitudes. ii), Transition temperature range, 207 < T < 214 K: the amplitude of the slow phase decreases to zero with a compensatory rise in the fast phase amplitude, with increasing temperature. iii), High temperature range, T > or = 214 K: the decay is monoexponential. The observed first-order rate constants for the monoexponential (k(obs,m)) and the fast phase of the biexponential decay (k(obs,f)) adhere to the same linear relation on an lnk versus T(-1) (Arrhenius) plot. Thus, k(obs,m) and k(obs,f) correspond to the same apparent Arrhenius prefactor and activation energy (logA(app,f) (s(-1)) = 13.0, E(a,app,f) = 15.0 kcal/mol), and therefore, a common decay mechanism. We propose that k(obs,m) and k(obs,f) represent the native, forward reaction of the substrate through the radical rearrangement step. The slow phase rate constant (k(obs,s)) for 190 < or = T < or = 207 K obeys a different linear Arrhenius relation (logA(app,s) (s(-1)) = 13.9, E(a,app,s) = 16.6 kcal/mol). In the transition temperature range, k(obs,s) displays a super-Arrhenius increase with increasing temperature. The change in E(a,app,s) with temperature and the narrow range over which it occurs suggest an origin in a liquid/glass or dynamical transition. A discontinuity in the activation barrier for the chemical reaction is not expected in the transition temperature range. Therefore, the transition arises from a change in the properties of the protein. We propose that a protein dynamical contribution to the reaction, which is present above the transition temperature, is lost below the transition temperature, owing to an increase in the activation energy barrier for protein motions that are coupled to the reaction. For both the fast and slow phases of the low temperature decay, the dynamical transition in protein motions that are obligatorily coupled to the reaction of the Co(II)-substrate radical pair lies below 190 K.
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Schwartz PA, Frey PA. 5'-Peroxyadenosine and 5'-peroxyadenosylcobalamin as intermediates in the aerobic photolysis of adenosylcobalamin. Biochemistry 2007; 46:7284-92. [PMID: 17503776 PMCID: PMC2553253 DOI: 10.1021/bi700077v] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
The photolysis of adenosylcobalamin (coenzyme B12) results in homolytic cleavage of the Co-C5' bond, forming cob(II)alamin and the 5'-deoxyadenosyl radical. In the presence of molecular oxygen, it has been proposed that the primary reaction is interception of the 5'-deoxyadenosyl radical by O2 to form adenosine-5'-aldehyde as the product (Hogenkamp, H. P. C., Ladd, J. N., and Barker, H. A. (1962) J. Biol. Chem. 237, 1950-1952). 5'-Peroxyadenosine is here found to be the initial nucleoside product of this reaction and found to decompose to adenosine-5'-aldehyde. Evidence indicates that 5'-peroxyadenosine arises from the hydrolysis of 5'-peroxyadenosylcobalamin, with the formation of cob(III)alamin. 5'-Peroxyadenosine undergoes further decomposition to adenosine-5'-aldehyde as the major final product of aerobic photolysis as well as to adenosine and adenine as minor products. In a cobalamin-dependent process, 5'-peroxyadenosine becomes re-ligated to cob(III)alamin to form 5'-peroxyadenosylcobalamin, which quickly decomposes to adenosine-5'-aldehyde and cob(III)alamin. This is supported by spectrophotometric observations of both rapidly photolyzed adenosylcobalamin and the reaction of cob(III)alamin with excess 5'-peroxyadenosine. 5'-Peroxyadenosine also slowly undergoes cobalamin-independent decomposition to adenosine-5'-aldehyde and the minor products adenosine and adenine. The present study provides a detailed description of the products initially formed when aqueous, homolytically cleaved adenosylcobalamin reacts with molecular oxygen and provides a detailed description of the behavior of those products subsequent to photolysis.
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Affiliation(s)
| | - Perry A. Frey
- To whom correspondence should be addressed. Department of Biochemistry, University of Wisconsin-Madison, 1710 University Ave., Madison, WI 53726, USA; Tel: (608) 262-0055. Fax: (608) 265-2904. E-mail:
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Szaciłowski K, Macyk W, Drzewiecka-Matuszek A, Brindell M, Stochel G. Bioinorganic photochemistry: frontiers and mechanisms. Chem Rev 2005; 105:2647-94. [PMID: 15941225 DOI: 10.1021/cr030707e] [Citation(s) in RCA: 559] [Impact Index Per Article: 29.4] [Reference Citation Analysis] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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35
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Chen H, Li G, Zhang FF, Sun L, Chen HL, Zhang SY. Co-C bond dissociation energy and reaction volume change of 2',5'-dideoxyadenosylcobalamin studied by laser-induced time-resolved photoacoustic calorimetry. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2003; 59:2767-2774. [PMID: 14499837 DOI: 10.1016/s1386-1425(03)00057-x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Time resolved photoacoustic calorimetry (PAC) was applied to a study of the photolysis of a coenzyme B(12) analog 2',5'-dideoxyadenosylcobalamin, which lacks an -OH group at the 2' position of ribofuranose ring. In aqueous solution, we report for the first time the quantum yield Phi(d) (0.25+/-0.02), Co-C bond dissociation energy (BDE; 31.8+/-2.5 kcal mol(-1)) and reaction volume change deltaV(R) (6.5+/-0.5 ml mol(-1)) due to conformation changes of the corrin ring and its side chains accompanying the cleavage of the Co-C bond. These values for the analog are very similar to those for the natural cofactor. Based our results and previous studies, a possible explanation for the similarity in their structure and properties versus the large difference in their enzymatic activity is discussed.
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Affiliation(s)
- Hao Chen
- Department of Chemistry, Nanjing University, Hankou Road 22, Nanjing 210093, People's Republic of China
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Blaauw R, Kingma IE, Werner WL, Wolowiec S, van der Baan JL, Balt S, Bickelhaupt F, de Bolster MW, Klumpp GW. Intramolecularly alkylated Cosalen complexes: thermolysis and photolysis of coenzyme B12 models with a cobalt-to-ligand carbon bridge. Inorganica Chim Acta 1998. [DOI: 10.1016/s0020-1693(97)05762-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Kruppa AI, Taraban MB, Leshina TV, Natarajan E, Grissom CB. CIDNP in the Photolysis of Coenzyme B12 Model Compounds Suggesting That C−Co Bond Homolysis Occurs from the Singlet State. Inorg Chem 1997. [DOI: 10.1021/ic960562c] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Hua Zhu B, Hua Liu Z, Yan H, Liu J, Chen H. The Coenzyme B12 analogs — ribosylcobalamins: Synthesis, characterization, and photolysis studies. J Inorg Biochem 1997. [DOI: 10.1016/s0162-0134(96)00077-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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Jarrett JT, Drennan CL, Amaratunga M, Scholten JD, Ludwig ML, Matthews RG. A protein radical cage slows photolysis of methylcobalamin in methionine synthase from Escherichia coli. Bioorg Med Chem 1996; 4:1237-46. [PMID: 8879545 DOI: 10.1016/0968-0896(96)00119-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Methionine synthase from Escherichia coli is a B12-dependent enzyme that utilizes a methylcobalamin prosthetic group. In the catalytic cycle, the methyl group of methylcobalamin is transferred to homocysteine, generating methionine and cob(I)-alamin, and cob(I)alamin is then remethylated by a methyl group from methyltetrahydrofolate. Methionine synthase occasionally undergoes side reactions that produce the inactive cob(II)alamin form of the enzyme. One such reaction is photolytic homolysis of the methylcobalamin C-Co bond. Binding to the methionine synthase apoenzyme protects the methylcobalamin cofactor against photolysis, decreasing the rate of this reaction by approximately 50-fold. The X-ray structure of the cobalamin-binding region of methionine synthase suggests how the protein might protect the methylcobalamin cofactor in the resting enzyme. In particular, the upper face (methyl or beta face) of the cobalamin cofactor is in contact with several hydrophobic residues provided by an alpha-helical domain, and these residues could slow photolysis by caging the methyl radical and favoring recombination of the CH3./cob(II)alamin radical pair. We have introduced mutations at three positions in the cap domain; phenylalanine 708, phenylalanine 714, and leucine 715 have each been replaced by alanine. Calculations based on the wild-type structure predict that two of these three mutations (Phe708Ala and Leu715Ala) will increase solvent accessibility to the methylcobalamin cofactor, and in fact these mutations result in dramatic increases in the rate of photolysis. The third mutation, Phe714Ala, is not predicted to increase the accessibility of the cofactor and has only a modest effect on the photolysis rate of the enzyme. These results confirm that the alpha-helical domain covers the cofactor in the resting methylcobalamin enzyme and that residues from this domain can protect the enzyme against photolysis. Further, we show that binding the substrate methyltetrahydrofolate to the wild-type enzyme results in a saturable increase in the rate of photolysis, suggesting that substrate binding induces a conformational change in the protein that increases the accessibility of the methylcobalamin cofactor.
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Affiliation(s)
- J T Jarrett
- Biophysics Research Division, University of Michigan, Ann Arbor 48109, USA
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Natarajan E, Grissom CB. The origin of magnetic field dependent recombination in alkylcobalamin radical pairs. Photochem Photobiol 1996; 64:286-95. [PMID: 8760570 DOI: 10.1111/j.1751-1097.1996.tb02460.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Magnetic field effect studies of alkylcobalamin photolysis provide evidence for the formation of a reactive radical pair that is born in the singlet spin state. The radical pair recombination process that is responsible for the magnetic field dependence of the continuous-wave (CW) quantum yield is limited to the diffusive radical pair. Although the geminate radical pair of adenosylcob(III)alamin also undergoes magnetic field dependent recombination (A.M. Chagovetz and C. B. Grissom, J. Am. Chem. soc. 115, 12152-12157, 1993), this process does not account for the magnetic field dependence of the CW quantum yield that is only observed in viscous solvents. Glycerol and ethylene glycol increase the microviscosity of the solution and thereby increase the lifetime of the spin-correlated diffusive radical pair. This enables magnetic field dependent recombination among spin-correlated diffusive radical pairs in the solvent cage. Magnetic field dependent recombination is not observed in the presence of nonviscosigenic alcohols such as isopropanol, thereby indicating the importance of the increased microviscosity of the medium. Paramagnetic radical scavengers that trap alkyl radicals that escape the solvent cage do not diminish the magnetic field effect on the CW quantum yield, thereby ruling out radical pair recombination among randomly diffusing radical pairs, as well as excluding the involvement of solvent-derived radicals. Magnetic field dependent recombination among alkylcobalamin radical pairs has been simulated by a semi-classical model of radical pair dynamics and recombination. These calculations support the existence of a singlet radical pair precursor.
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Affiliation(s)
- E Natarajan
- Department of Chemistry, University of Utah, Salt Lake City 84112, USA
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Affiliation(s)
- J P Glusker
- Institute for Cancer Research, Fox Chase Cancer Center, Philadelphia, Pennsylvania 19111
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Frisbie SM, Chance MR. Human cobalophilin: the structure of bound methylcobalamin and a functional role in protecting methylcobalamin from photolysis. Biochemistry 1993; 32:13886-92. [PMID: 8268164 DOI: 10.1021/bi00213a018] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The interactions of methylcobalamin with cobalophilin from human serum were analyzed using extended X-ray absorption fine structure (EXAFS) spectroscopy, photolysis of the cobalt-carbon bond of methylcobalamin, and a pKa determination of the protonation of the coordinated nitrogen of 5,6-dimethylbenzimidazole (DMB). These results are consistent with the idea that the DMB nitrogen is still coordinated when protein is bound; however, the ability of a methyl radical (generated by photolysis) to escape the geminate cage of the protein is considerably reduced. For methylcobalamin in solution, the DMB nitrogen ligand is at a distance of 2.20 +/- 0.03 A from cobalt [Sagi, I., & Chance, M. R. (1992) J. Am. Chem. Soc. 114, 8061-8066]. This distance to the lower axial ligand does not change when protein binds (2.20 +/- 0.04 A), nor do the optical spectra exhibit any base-off character. The average of the distance from cobalt to the four equatorial nitrogens of the corrin plane is also unchanged. The pKa for the conversion of the "base-on" to the "base-off" form of methylcobalamin, where the above DMB nitrogen becomes protonated and the Co-N axial bond is cleaved, does not deviate from the free cobalamin value of 2.7 when methylcobalamin is bound to cobalophilin. These results indicate that replacement of the DMB ligand with a ligand from the protein is unlikely. Although the background-subtracted EXAFS data sets for free methylcobalamin and for the protein complex are extremely similar, more accurate data with explicit higher shell analysis would be required to entirely rule out ligand replacement. The chemical and electronic nature of the ligand changes little.(ABSTRACT TRUNCATED AT 250 WORDS)
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Affiliation(s)
- S M Frisbie
- Department of Chemistry, Georgetown University, Washington, D.C. 20057
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