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Affiliation(s)
- Felipe Curtolo
- Department of Biochemistry, Instituto de Quı́mica, Universidade de São Paulo, Av. Prof. Lineu Prestes 748, 05508-900 São Paulo, SP, Brazil
| | - Guilherme M. Arantes
- Department of Biochemistry, Instituto de Quı́mica, Universidade de São Paulo, Av. Prof. Lineu Prestes 748, 05508-900 São Paulo, SP, Brazil
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Abstract
This account describes the application of kinetic isotope effects (KIEs) to investigate the mechanistic properties of flavin dependent enzymes. Assays can be conducted during steady-state catalytic turnover of the flavoenzyme with its substrate or by using rapid-kinetic techniques to measure either the reductive or oxidative half-reactions of the enzyme. Great care should be taken to ensure that the observed effects are due to isotopic substitution and not other factors such as pH effects or changes in the solvent viscosity of the reaction mixture. Different types of KIEs are described along with a physical description of their origins and the unique information each can provide about the mechanism of an enzyme. Detailed experimental techniques are outlined with special emphasis on the proper controls and data analysis that must be carried out to avoid erroneous conclusions. Examples are provided for each type of KIE measurement from references in the literature. It is our hope that this article will clarify any confusion concerning the utility of KIEs in the study of flavoprotein mechanism and encourage their use by the community.
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Robbins JM, Geng J, Barry BA, Gadda G, Bommarius AS. Photoirradiation Generates an Ultrastable 8-Formyl FAD Semiquinone Radical with Unusual Properties in Formate Oxidase. Biochemistry 2018; 57:5818-5826. [PMID: 30226367 DOI: 10.1021/acs.biochem.8b00571] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Formate oxidase (FOX) was previously shown to contain a noncovalently bound 8-formyl FAD (8-fFAD) cofactor. However, both the absorption spectra and the kinetic parameters previously reported for FOX are inconsistent with more recent reports. The ultraviolet-visible (UV-vis) absorption spectrum reported in early studies closely resembles the spectra observed for protein-bound 8-formyl flavin semiquinone species, thus suggesting FOX may be photosensitive. Therefore, the properties of dark and light-exposed FOX were investigated using steady-state kinetics and site-directed mutagenesis analysis along with inductively coupled plasma optical emission spectroscopy, UV-vis absorption spectroscopy, circular dichroism spectroscopy, liquid chromatography and mass spectrometry, and electron paramagnetic resonance (EPR) spectroscopy. Surprisingly, these experimental results demonstrate that FOX is deactivated in the presence of light through generation of an oxygen stable, anionic (red) 8-fFAD semiquinone radical capable of persisting either in an aerobic environment for multiple weeks or in the presence of a strong reducing agent like sodium dithionite. Herein, we study the photoinduced formation of the 8-fFAD semiquinone radical in FOX and report the first EPR spectrum of this radical species. The stability of the 8-fFAD semiquinone radical suggests FOX to be a model enzyme for probing the structural and mechanistic features involved in stabilizing flavin semiquinone radicals. It is likely that the photoinduced formation of a stable 8-fFAD semiquinone radical is a defining characteristic of 8-formyl flavin-dependent enzymes. Additionally, a better understanding of the radical stabilization process may yield a FOX enzyme with more robust activity and broader industrial usefulness.
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Affiliation(s)
- John M Robbins
- School of Chemical and Biomolecular Engineering , Georgia Institute of Technology , Atlanta , Georgia 30332-0100 , United States.,Engineered Biosystems Building (EBB) , Georgia Institute of Technology , Atlanta , Georgia 30332-2000 , United States
| | - Jiafeng Geng
- School of Chemistry and Biochemistry, Parker H. Petit Institute of Bioengineering and Bioscience , Georgia Institute of Technology , Atlanta , Georgia 30332-0363 , United States
| | - Bridgette A Barry
- School of Chemistry and Biochemistry, Parker H. Petit Institute of Bioengineering and Bioscience , Georgia Institute of Technology , Atlanta , Georgia 30332-0363 , United States
| | - Giovanni Gadda
- Department of Chemistry , Georgia State University , Atlanta , Georgia 30302-3965 , United States.,Center for Diagnostics and Therapeutics , Georgia State University , Atlanta , Georgia 30302-3965 , United States.,Center for Biotechnology and Drug Design , Georgia State University , Atlanta , Georgia 30302-3965 , United States.,Department of Biology , Georgia State University , Atlanta , Georgia 30302-3965 , United States
| | - Andreas S Bommarius
- School of Chemical and Biomolecular Engineering , Georgia Institute of Technology , Atlanta , Georgia 30332-0100 , United States.,Engineered Biosystems Building (EBB) , Georgia Institute of Technology , Atlanta , Georgia 30332-2000 , United States.,School of Chemistry and Biochemistry, Parker H. Petit Institute of Bioengineering and Bioscience , Georgia Institute of Technology , Atlanta , Georgia 30332-0363 , United States
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