摘要:

Optimal steroidogenic capacity in the adrenal cortex is regulated by ACTH via cAMP and involves transcription of the genes encoding the adrenocortical steroid hydroxylases. The microsomal steroid hydroxylases, P45017αand P450C21, are encoded byCYP17andCYP21, respectively. These genes are thought to have arisen from a common progenitor gene and are coordinately regulated by ACTH. The cAMP responsive sequences (CRS) located in the 5′‐flanking regions of these genes are distinct from one another and from known consensus sequences imparting cAMP responsiveness in other genes. TheCYP21CRS binds a putative adrenal‐specific nuclear protein. In contrast, theCYP17CRSI binds a ubiquitous protein that is apparently active only in steroidogenic cells. Thus the ACTH‐dependent transcription of these two genes, which have a common evolutionary origin and are coordinately expressed in the adrenal cortex, involves distinct biochemical mechanisms.—Zanger, U. M.; Kagawa, M.; Lund, J.; Waterman, M. R. Distinct biochemical mechanisms for cAMP‐dependent transcription ofCYP17andCYP21.FASEB J.6: 719‐723; 1992.

ISSN:0892-6638    

DOI:10.1096/fasebj.6.2.1311271

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

We are constantly exposed to many potentially toxic chemicals. Most require metabolic activation to species responsible for cell injury. Although cytochrome P450 2E1 is only one of many different forms of cytochrome P450 that catalyze these reactions, it has an important role in human health as a result of being readily induced by acute and chronic alcohol ingestion. The enzyme efficiently catalyzes the lowKmmetabolism of compounds commonly used as solvents in industry and at home as well as components found in cigarette smoke, many of which are established carcinogens and hepatotoxins. As a result, there is the potential for increased risk to low level exposure to such chemicals while cytochrome P450 2E1 is induced. Many substrates have been identified for cytochrome P450 2E1. Of the 52 substrates for the enzyme identified in this review, the demethylation ofN,N‐dimethylnitrosamine and the hydroxylation ofp‐nitrophenol and chlorzoxazone are the most effective for monitoring the level of this enzyme. In addition to oxidative reactions, cytochrome P450 2E1 is also an efficient catalyst of reductive reactions. CCl4‐induced hepatotoxicity is one of the best‐documented cases for the participation of cytochrome P450 2E1 in a toxicologically important reductive reaction. The reduction of oxygen to superoxide and peroxide are also important reductive reactions of the enzyme and could be important in lipid peroxidation. However, the role of this reaction in vivo remains controversial.—Koop, D. R. Oxidative and reductive metabolism by cytochrome P450 2E1.FASEB J.6: 724‐730; 1992.

ISSN:0892-6638    

DOI:10.1096/fasebj.6.2.1537462

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Arachidonic acid and many products of the arachidonate cascade serve as substrates for cytochrome P450‐mediated metabolism via allylic oxidation, omega hydroxylation, and epoxygenation as well as peroxide rearrangement. Defining the physiological importance of these metabolites is an area of intense research interest. Cytochrome P450‐catalyzed reactions play prominent roles in multiplying the structural and functional diversity of the arachidonate metabolic cascade.—Capdevila, J. H.; Falck, J. R.; Estabrook, R. W. Cytochrome P450 and the arachidonate cascade.FASEB J.6: 731‐736; 1992.

ISSN:0892-6638    

DOI:10.1096/fasebj.6.2.1537463

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

The levels and activities of cytochrome P450 enzymes are influenced by a variety of factors, including the diet. In this article, the effects of selected non‐nutritive dietary chemicals, macronutrients, micronutrients, and ethanol on cytochromes P450 and xenobiotic metabolism are reviewed in the light of our current understanding of the multiplicity and substrate specificity of cytochrome P450 enzymes. Although the mechanisms of action of several dietary chemicals on specific cytochrome P450 isozymes have been established, those for macro‐ and micronutrients are largely unknown. It is known, however, that specific nutrients may have varied effects on different cytochrome P450 forms and thus may affect the metabolism of various drugs differently. Nutritional deficiencies generally cause lowered rates of xenobiotic metabolism. In certain cases, such as thiamin deficiency and mild riboflavin deficiency, however, enhanced rates of metabolism of xenobiotics were observed. The effects of dietary modulation of xenobiotic metabolism on chemical toxicity and carcinogenicity are discussed.—Yang, C. S.; Brady, J. F.; Hong, J.‐Y. Dietary effects on cytochromes P450, xenobiotic metabolism, and toxicity.FASEB J.6: 737‐744; 1992.

ISSN:0892-6638    

DOI:10.1096/fasebj.6.2.1537464

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Many biochemical approaches have been applied to the human cytochrome P450 enzymes, and more than 20 different gene products have been characterized with regard to their properties and catalytic specificities. The complement of the various cytochrome P450 enzymes in a given individual varies markedly, and dramatic differences may be seen in drug metabolism, pharmacological response, and susceptibility to toxic effects. An understanding of the nature of the individual cytochrome P450 enzymes and their regulation should be useful in determining the most suitable animal models, ascertaining risk from chemicals, and in avoiding undesirable drug interactions.—Guengerich, F, P. Characterization of human cytochrome P450 enzymes.FASEB J.6: 745‐748; 1992.

ISSN:0892-6638    

DOI:10.1096/fasebj.6.2.1537465

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Polar amino acids in the (putative) distal site are well conserved in P450s. For example, Glu318 for P450dis well conserved as either Glu or Asp for P450s, and Thr319 for P450dis also conserved for P450s. We have studied how mutations at Glu318 and Thr319 of P450dinfluence the catalytic activity toward methanol associated with the activation of O2. Catalytic activities of Glu318Asp, Glu318Ala, and Thr319Ala mutants toward methanol were 60, 25, and 38%, respectively, compared with that of the wild type. O2consumption and NADPH oxidation rates of each mutants varied corresponding to the catalytic activities. However, surprisingly, efficiency (16–40%) of incorporated O to the substrate vs. consumed O2for the Glu318Ala and Thr319Ala mutants were higher than that (9%) of the wild type. In addition, H2O2, which is produced from uncoupling for the wild‐type P450d, was not observed for reaction of the Glu318Ala and Thr319Ala mutants. It seemed that consumed O2was partially reduced to 2 mol of H2O by 4‐electron transfer from NADPH for the wild‐type and Thr319Ala mutant. However, for the two Glu318 mutants, it appeared that the consumed O2was not reduced in the same way. It was thus suggested that the conserved Glu318 and Thr319 of P450dare not essential for the activation of O2in the methanol oxidation. Role of the water molecule or the methanol molecule in the catalytic function was implied.—Hiroya, K.; Ishigooka, M.; Shimizu, T.; Hatano, M. Role of Gly318 and Thr319 in the catalytic function of cytochrome P450d: effects of mutations on the methanol hydroxylation.FASEB J.6: 749‐751; 1992.

ISSN:0892-6638    

DOI:10.1096/fasebj.6.2.1347023

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

The expression of several forms of cytochrome P450 including P450 1A2, 2D6, 2E1, and 3A was investigated in human hepatocytes maintained in primary culture for 96 h in the absence or presence of 50μmof various imidazole derivatives. These included ketoconazole, clotrimazole, miconazole, fluconazole, secnidazole and metronidazole. In addition, the typical inducers rifampicin andβ‐naphthoflavone were used for comparison. Western and Northern blot analysis of microsomes and RNA prepared from these cultures as well as de novo synthesis experiments revealed that, among the imidazole derivatives tested, only clotrimazole was a strong rifampicin‐like inducer of P450 3A. The expression of the other forms of P450 tested was not affected by the treatments. Analysis of the inhibition of 13 monoxygenase activities, including ethoxyresorufin and phenacetin O‐deethylases, coumarin7α‐, lauric acid 11‐ and 12‐, mephenytoin 4‐, debrisoquin 4‐, and aniline hydroxylases, benzphetamine, aminopyrine, mephenytoin and erythromycin demethylases, and cyclosporin oxidase (representative of 10 different forms of P450 in human liver microsomes) revealed that ketoconazole was a strong and selective in vitro inhibitor of P450 3A (cyclosporin oxidase) with aKi<1μm. Clotrimazole and miconazole were also strong inhibitors of P450 3A‐mediated activities in contrast to the other imidazole derivatives.—Maurice, M.; Pichard, L.; Daujat, M.; Fabre, I.; Joyeux, H.; Domergue, J.; Maurel, P. Effects of imidazole derivatives on cytochromes P450 from human hepatocytes in primary culture.FASEB J.6: 752‐758; 1992.

ISSN:0892-6638    

DOI:10.1096/fasebj.6.2.1371482

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Enzymatically active human cytochrome P450 1A2 was expressed inEscherichia coliutilizing the pCWori+ vector containing a modified cDNA. The coding sequence for the NH2‐terminal region of the protein was modified by the alignment and substitution of a 27 bp segment from a modified bovine P450 17A1 cDNA onto the 5′ end of the open reading frame of P450 1A2 at amino acid 21. The expressed chimeric P450 was produced at a high level in a functionally intact form, as assayed by the formation in vivo of the 449 nm absorbance band of the CO complex of the reduced hemoprotein.E. colimembrane preparations were shown to contain P450 1A2, which was active in the 2‐hydroxylation of estradiol, and the O‐deethylation of7‐ethoxycoumarin and7‐ethoxyresorufin, when reconstituted with recombinant rat liver NADPH‐cytochrome P450 reductase.—Fisher, C. W.; Caudle, D. L.; Martin‐Wixtrom, C.; Quattrochi, L. C.; Tukey, R. H.; Waterman, M. R.; Estabrook, R. W. High‐level expression of functional human cytochrome P450 1A2 inEscherichia coli.FASEB J.6: 759‐764; 1992.

ISSN:0892-6638    

DOI:10.1096/fasebj.6.2.1537466

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Glycerol can be oxidized by rat liver microsomes to formaldehyde in a reaction that requires the production of reactive oxygen intermediates. Studies with inhibitors, antibodies, and reconstituted systems with purified cytochrome P4502E1 were carried out to evaluate whether P450 was required for glycerol oxidation. A purified system containing phospholipid, NADPH‐cytochrome P450 reductase, P4502E1, and NADPH oxidized glycerol to formaldehyde. Formaldehyde production was dependent on NADPH, reductase, and P450, but not phospholipid. Formaldehyde production was inhibited by substrates and ligands for P4502E1, as well as by anti‐pyrazole P4502E1 IgG. The oxidation of glycerol by the reconstituted system was sensitive to catalase, desferrioxamine, and EDTA but not to superoxide dismutase or mannitol, indicating a role for H2O2plus non‐heme iron, but not superoxide or hydroxyl radical in the overall glycerol oxidation pathway. The requirement for reactive oxygen intermediates for glycerol oxidation is in contrast to the oxidation of typical substrates for P450. In microsomes from pyrazole‐treated, but not phenobarbital‐treated rats, glycerol oxidation was inhibited by anti‐pyrazole P450 IgG, anti‐hamster ethanol‐induced P450 IgG, and monoclonal antibody to ethanol‐induced P450, although to a lesser extent than inhibition of dimethylnitrosamine oxidation. Anti‐rabbit P4503a IgG did not inhibit glycerol oxidation at concentrations that inhibited oxidation of dimethylnitrosamine. Inhibition of glycerol oxidation by antibodies and by aminotriazole and miconazole was closely associated with inhibition of H2O2production. These results indicate that P450 is required for glycerol oxidation to formaldehyde; however, glycerol is not a direct substrate for oxidation to formaldehyde by P450 but is a substrate for an oxidant derived from interaction of iron with H2O2generated by cytochrome P450.—Clejan, L. A.; Cederbaum, A. I. Role of cytochrome P450 in the oxidation of glycerol by reconstituted systems and microsomes.FASEB J.6: 765‐770; 1992.

ISSN:0892-6638    

DOI:10.1096/fasebj.6.2.1537467

出版商:Wiley    

年代:1992

数据来源: WILEY

摘要:

Microsomal 4‐hydroxylase of 1,2,3,4‐tetrahydroisoquinoline (TIQ), a possible candidate for causing Parkinson disease, was characterized by using rat hepatic microsomes and purified P450 isozymes. Kinetic analysis revealed thatKmandVmaxvalues (mean ±se) for hepatic microsomal TIQ 4‐hydroxylase of male Wistar rats were 319.6 ± 26.8μmand 12.13±1.43 pmol·min–1·mg–1protein, respectively. When TIQ 4‐hydroxylase activity was compared in Wistar (an animal model of extensive debrisoquine metabolizers) and Dark Agouti (an animal model of poor debrisoquine metabolizers) rats, significant strain (Wistar>Dark Agouti) and sex (male>female) differences were observed. The microsomal activity toward TIQ 4‐hydroxylation was increased by pretreatment of male Wistar rats with P448 inducers (β‐naphthoflavone and sudan I), but not with phenobarbital. Pretreatment with propranolol, an inhibitor of P450 isozymes belonging to the P450 IID gene subfamily, decreased TIQ 4‐hydroxylase activity. P450 BTL, a P450 isozyme belonging to the IID subfamily, showed TIQ 4‐hydroxylase activity of 64.1 pmol · min–1· nmol P450–1, which was 3.2‐fold that of microsomes (20.9 pmol · min–1· nmol P450–1). Antibody (IgG) against this isozyme suppressed microsomal TIQ 4‐hydroxylase activity concentration‐dependently. A male‐specific P450 ml (P450IIC11) catalyzed this reaction to a much lesser extent (10.0 pmol·min–1·nmol P450–1), and its antibody did not affect the microsomal activity. These results suggest that TIQ 4‐hydroxylation in hepatic microsomes are catalyzed predominantly by a P450 isozyme (or isozymes) belonging to the IID gene subfamily in non‐treated rats and its immunochemically related P450 isozyme (or isozymes), and that a P450 isozyme (or isozymes) belonging to the IA subfamily also participates in TIQ 4‐hydroxylation in rats pretreated with P448‐inducers.—Suzuki, T.; Fujita, S.; Narimatsu, S.; Masubuchi, Y.; Tachibana, M.; Ohta, S.; Hirobe M. Cytochrome P450 isozymes catalyzing 4‐hydroxylation of parkinsonism‐related compound 1,2,3,4‐tetrahydroisoquinoline in rat liver microsomes.FASEB J.6: 771‐776; 1992.

ISSN:0892-6638    

DOI:10.1096/fasebj.6.2.1537468

出版商:Wiley    

年代:1992

数据来源: WILEY