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Shou M, Norcross R, Sandig G, Lu P, Li Y, Lin Y, Mei Q, Rodrigues AD, Rushmore TH. Substrate specificity and kinetic properties of seven heterologously expressed dog cytochromes p450. Drug Metab Dispos 2003; 31:1161-9. [PMID: 12920172 DOI: 10.1124/dmd.31.9.1161] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
Seven dog cytochromes p450 (p450s) were heterologously expressed in baculovirus-Sf21 insect cells. Of all enzymes examined, CYP1A1 exhibited high 7-ethoxyresorufin O-deethylase activity (low Km enzyme, 1 microM). CYP2B11 and CYP3A12 effectively catalyzed the N1-demethylation and C3-hydroxylation of diazepam (and its derivatives), whereas CYP3A12 and CYP2D15 catalyzed exclusively the N- and O-demethylation, respectively, of dextromethorphan. However, no saturation velocity curves for the N-demethylation of dextromethorphan (up to 500 microM) were achieved, suggesting a high Km for CYP3A12. In contrast to CYP3A12, the CYP2D15-dependent O-demethylation of dextromethorphan was a low Km process (Km = 0.7 microM), similar to that in dog liver microsomes (Km = 2.3 microM). CYP2D15 was also capable of metabolizing bufuralol (1'-hydroxylation), with a Km of 3.9 microM, consistent with that obtained with dog liver microsomes. CYP3A12 was shown to primarily oxidize testosterone at 16alpha-, 2alpha/2beta-, and 6beta-positions. Selectivity of CYP3A12 was observed toward testosterone 6beta-(Km = 83 microM) and 2alpha/2beta-hydroxylations (Km = 154 microM). However, the 16alpha-hydroxylation of testosterone was catalyzed by CYP2C21 also (Km = 6.4 microM for CYP2C21). Therefore, the 6beta- and 16alpha-hydroxylation of testosterone can potentially be employed as markers of CYP3A12 and CYP2C21 (at low concentration), respectively. CYP2C21 was also capable of catalyzing diclofenac 4'-hydroxylation, although some activity was detected with CYP2B11. Surprisingly, none of the p450s selectively metabolized (S)-mephenytoin 4'-hydroxylation. The results described herein are a first step toward the systematic evaluation of a panel of dog p450s and the development of dog p450 isoenzyme-selective marker substrates, as well as providing useful information on prediction and extrapolation of the results from in vitro to in vivo and from dog to human.
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Affiliation(s)
- Magang Shou
- Department of Drug Metabolism, Merck Research Laboratories, West Point, PA 19486, USA.
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Goosen TC, Kent UM, Brand L, Hollenberg PF. Inactivation of cytochrome P450 2B1 by benzyl isothiocyanate, a chemopreventative agent from cruciferous vegetables. Chem Res Toxicol 2000; 13:1349-59. [PMID: 11123978 DOI: 10.1021/tx000133y] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
A series of arylalkyl isothiocyanates were evaluated for their ability to inactivate purified cytochrome P450 2B1 in a reconstituted system. Benzyl isothiocyanate (BITC) and phenethyl isothiocyanate (PEITC) occur naturally in several cruciferous vegetables, and the inhibition of cytochrome P450 (P450) enzymes has been implicated in their chemopreventative abilities. The naturally occurring isothiocyanates BITC and PEITC inactivated P450 2B1 in a time- and concentration-dependent manner, whereas the synthetic isothiocyanates phenylpropyl and phenylhexyl isothiocyanate did not result in inactivation, but were potent competitive inhibitors of P450 2B1 activity. The kinetics of inactivation of P450 2B1 by BITC were characterized. The 7-ethoxy-4-(trifluoromethyl)coumarin O-deethylation activity of P450 2B1 was inactivated in a mechanism-based manner. The loss of O-deethylation activity followed pseudo-first-order kinetics, was saturable, and required NADPH. The BITC concentration required for half-maximal inactivation (K(I)) was 5.8 microM, and the maximal rate constant for inactivation was 0.66 min(-)(1) at 23 degrees C. BITC was a very efficient inactivator of P450 2B1 with a partition ratio of approximately 9. The mechanism of BITC-mediated inactivation of P450 2B1 was also investigated. More than 80% of the catalytic activity was lost within 12 min with a concomitant loss of approximately 45% in the ability of the reduced enzyme to bind CO. The magnitude of the UV/visible absorption spectrum of the inactivated protein did not decrease significantly, and subsequent HPLC analysis indicated no apparent modification of the heme. HPLC and protein precipitation analyses indicated that the P450 apoprotein was covalently modified by a metabolite of BITC. Determination of the binding stoichiometry indicated that 0.90 +/- 0. 16 mol of radiolabeled metabolite was bound per mole of enzyme that was inactivated, suggesting the modification of a single amino acid residue per molecule of enzyme that was inactivated. The results reported here indicate that BITC is a mechanism-based inactivator of P450 2B1 and that inactivation occurs primarily through protein modification.
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Affiliation(s)
- T C Goosen
- Department of Pharmacology, Potchefstroom University for Christian Higher Education, Potchefstroom 2520, South Africa
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Shou M, Lu T, Krausz KW, Sai Y, Yang T, Korzekwa KR, Gonzalez FJ, Gelboin HV. Use of inhibitory monoclonal antibodies to assess the contribution of cytochromes P450 to human drug metabolism. Eur J Pharmacol 2000; 394:199-209. [PMID: 10771285 DOI: 10.1016/s0014-2999(00)00079-0] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Three inhibitory monoclonal antibodies specific to cytochrome P450 3A4/5 (CYP3A4/5), CYP2C8/9/19 and CYP2E1, respectively, were used to assess the contribution of the P450s to the metabolism of seven substrates in liver microsomes from 18 human donors, as measured by monoclonal antibody inhibition phenotyping of the substrate conversion to product(s). Metabolism of seven substrates by recombinant cytochromes P450 and human liver microsomes was performed in the presence of monoclonal antibodies and their metabolites were analyzed by high-performance liquid chromatography (HPLC) or gas chromatography-mass spectrophotometry (GC-MS) to measure the magnitude of inhibition. Our results showed that CYP3A4/5 contributes to testosterone 6beta-hydroxylation, taxol phenol formation, diazepam 3-hydroxylation, diazepam N-demethylation, and aflatoxin B1 3-hydroxylation in human liver by 79.2%, 81.5%, 73. 2%, 34.5% and 80%, respectively. CYP2E1 contributes to chlorzoxazone 6-hydroxylation, p-nitroanisole O-demethylation, and toluene hydroxylation by 45.8%, 27.7% and 44.2% respectively, and CYP2C8/9/19 contribute to diazepam N-demethylation by 30.6%. The additive contribution (75.3%) of human CYP3A and CYP2C to diazepam N-demethylation was also observed in the presence of both anti-CYP3A4/5 and anti-CYP2C8/9/19 monoclonal antibodies. The contribution of individual P450s to the specific metabolic reaction in human liver varies greatly in the individual donors and the substrates examined. Thus, inhibitory monoclonal antibodies could play a unique role in defining the single or subfamily of cytochrome P450 that is responsible for the metabolism of specific drugs.
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Affiliation(s)
- M Shou
- Department of Drug Metabolism, WP75A-203, Merck Research Laboratories, West Point, PA 19486, USA.
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Gelboin HV, Krausz KW, Goldfarb I, Buters JT, Yang SK, Gonzalez FJ, Korzekwa KR, Shou M. Inhibitory and non-inhibitory monoclonal antibodies to human cytochrome P450 3A3/4. Biochem Pharmacol 1995; 50:1841-50. [PMID: 8615863 DOI: 10.1016/0006-2952(95)02077-2] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Cytochromes P450 3A3/4 are inordinately important P450 enzymes catalyzing the metabolism of a large variety of clinically useful drugs, steroids, and carcinogens. Two monoclonal antibodies, MAb 3-29-9 and MAb 275-1-2, were prepared to human P450 3A4 from mice immunized with baculovirus-expressed human P450 3A4. MAb 3-29-9 was a powerful inhibitor of the enzymatic activity of P450 3A3/4/5. MAb 3-29-9 inhibited the P450 3A3, 3A4, and 3A5 catalyzed metabolism of substrates of divergent molecular weights, e.g., p-nitroanisole, phenanthrene, diazepam, testosterone, taxol, and cyclosporin. However, MAb 3-29-9 did not give a western blot with P450 3A3 or 3A4. MAb 275-1-2 was non-inhibitory but yielded a strong western blot with P450 3A3 and 3A4 but not with 3A5, and thus distinguished between 3A3/4 and 3A5. The two MAbs did not cross-react with human 2E1, 1A2, 2B6, 2C8, and 2C9; rat 2A1, 3A1/2, 4A1, 4A3, and 2B1; and mouse 1A1 and 1A2. MAb 3-29-9 has been used successfully to measure the quantitative contribution of P450 3A3 and 3A4 to the metabolism of the above-designated substrates in human adult liver. MAb 3-29-9 and MAb 275-1-2 are precise and sensitive reagents for P450 3A studies.
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Affiliation(s)
- H V Gelboin
- Laboratory of Molecular Carcinogenesis, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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Shou M, Korzekwa KR, Crespi CL, Gonzalez FJ, Gelboin HV. Metabolism of Benzo[a]pyrene by Seven cDNA Expressed Human Cytochromes P450. Polycycl Aromat Compd 1994. [DOI: 10.1080/10406639408014706] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
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Peyronneau MA, Renaud JP, Jaouen M, Urban P, Cullin C, Pompon D, Mansuy D. Expression in yeast of three allelic cDNAs coding for human liver P-450 3A4. Different stabilities, binding properties and catalytic activities of the yeast-produced enzymes. EUROPEAN JOURNAL OF BIOCHEMISTRY 1993; 218:355-61. [PMID: 8269924 DOI: 10.1111/j.1432-1033.1993.tb18384.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Three natural allelic cDNAs coding for P-450 3A4, the major form in human liver, namely NF25, NF10 and hPCN1, have been expressed in Saccharomyces cerevisiae. NF25 and hPCN1 were functionally expressed in yeast microsomes, yielding proteins with an absorption maximum at 448 nm in the CO-reduced difference spectrum. Some catalytic activities and substrate binding properties of P-450 NF25 and P-450 hPCN1 in yeast microsomes have been compared; no striking difference was found, showing that the two point substitutions between their amino-acid sequences (Trp392 and Thr431 in P-450 NF25 are replaced by Val392 and Ile431 in P-450 hPCN1) have no significant effect on the functional properties of these two variants. By contrast, P-450 NF10, which differs from P-450 NF25 by a one-amino-acid deletion (Ile224 replacing Thr224-Val225), was produced as a denatured form, as revealed by an absorption maximum at 420 nm, and was not catalytically active. This suggests that the deletion prevents the correct folding of the protein. The results of this study show that P-450 NF25 and P-450 hPCN1 are two roughly equivalent, functionally active variants of P-450 3A4, but that P-450 NF10 is a defective, unstable gene product that could arise from an alternative mRNA splicing. This could contribute to the large variations reported for nifedipine oxidation, a typical P-450 3A4 activity, in human liver.
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Affiliation(s)
- M A Peyronneau
- Laboratoire de Chimie et Biochimie Pharmacologiques et Toxicologiques, CNRS URA 400, Université Paris 5, France
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Kedzie KM, Grimm SW, Chen F, Halpert JR. Hybrid enzymes for structure-function analysis of cytochrome P-450 2B11. BIOCHIMICA ET BIOPHYSICA ACTA 1993; 1164:124-32. [PMID: 8329443 DOI: 10.1016/0167-4838(93)90238-m] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Previous work has shown that P-450 2B11 is responsible for the unique ability of dogs to metabolize and eliminate certain highly-chlorinated biphenyls such as 2,2',4,4',5,5'-hexachlorobiphenyl (245-HCB), whereas the related P-450 2B forms in rat and rabbit are unable to metabolize the compound to any significant degree. To determine the structural basis for this functional diversity, hybrid enzymes were generated. Success with this approach required a careful choice of second enzyme and common substrate with which to assess the functional integrity of the hybrid proteins. The choices of P-450 2B5 from rabbit as the second enzyme and androstenedione as the substrate were based in part on the finding that P-450 2B11 and P-450 2B5 hydroxylate androstenedione with similar overall activities but distinct profiles. Enzymatic studies with eight hybrid enzymes provided evidence for two regions of P-450 2B11 and 2B5, between residues 95-239 and 240-370, that appear to be involved in defining substrate specificity for androstenedione, and three regions of P-450 2B11, between residues 95-239, 240-370, and 371-494, that contain amino acids necessary for metabolism of 245-HCB. This deliberate approach to the creation of hybrid cytochromes P-450 has generated a series of enzymes that will be central to further structure-function studies of the cytochromes P-450 2B.
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Affiliation(s)
- K M Kedzie
- Department of Pharmacology and Toxicology, College of Pharmacy, University of Arizona, Tucson 85721
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Koymans L, Donné-op den Kelder GM, Koppele Te JM, Vermeulen NP. Cytochromes P450: their active-site structure and mechanism of oxidation. Drug Metab Rev 1993; 25:325-87. [PMID: 8404461 DOI: 10.3109/03602539308993979] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Affiliation(s)
- L Koymans
- Department of Pharmacochemistry, Faculty of Chemistry, Free University, Amsterdam, The Netherlands
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Hanioka N, Gonzalez FJ, Lindberg NA, Liu G, Korzekwa KR. Chimeric cDNA expression and site directed mutagenesis studies of cytochrome P450s CYP2A1 and CYP2A2. J Steroid Biochem Mol Biol 1992; 43:1037-43. [PMID: 22217848 DOI: 10.1016/0960-0760(92)90331-c] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Construction of chimeras and site directed mutagenesis were used to study the regioselectivity and kinetics of testosterone hydroxylation by the cytochrome P450s CYP2A1 and CYP2A2. Although these enzymes exhibit 88% sequence similarity, they catalyze very different regioselective hydroxylations of testosterone. Active chimeras inwhich the first 355 amino acids do not correspond to a single enzyme show broad radioselectivity, whereas the specificity of the parent enzyme is obtained if the first 355 amino acids are unchanged. Therefore, the region between amino acids 275 and 355 is important in maintaining regioselectivity. Single point mutants were constructed for the 13 amino acid differences in this region. For 26 single point and 2 double mutants all active mutants have the same regioselectivity as the parent enzymes. However, kinetic analysis of the CYP2A1 mutants showed that 4 single point mutants and 1 double mutant had kinetic parameters very different from the parent enzyme. All of these substitutions are associated with the conserved dioxygen binding region of the putative I helix predicted from the crystal structure of P450(cam). Deuterium isotope effects were used to determine any changes in the rate of reduction and to estimate the relative amount of excess water formation. Changes in reduction rates are not sufficient to account for the differences in V(max) values. Therefore, it is likely that the amount of hydrogen peroxide formed is a primary determinant of V(max).
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Affiliation(s)
- N Hanioka
- Laboratory of Molecular Carcinogenesis, National Cancer Institute, Bethesda, MD 20892, USA
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Kedzie K, Balfour C, Escobar G, Grimm S, He Y, Pepperl D, Regan J, Stevens J, Halpert J. Molecular basis for a functionally unique cytochrome P450IIB1 variant. J Biol Chem 1991. [DOI: 10.1016/s0021-9258(18)54602-0] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
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