We provide here a list of 221 P450 genes and 12 putative pseudogenes that have been characterized as of December 14, 1992. These genes have been described in 31 eukaryotes (including 11 mammalian and 3 plant species) and 11 prokaryotes. Of 36 gene families so far described, 12 families exist in all mammals examined to date. These 12 families comprise 22 mammalian subfamilies, of which 17 and 15 have been mapped in the human and mouse genome, respectively. To date, each subfamily appears to represent a cluster of tightly linked genes. This revision supersedes the previous updates [Nebert et al., DNA 6, 1–11, 1987; Nebert et al., DNA 8, 1–13, 1989; Nebert et al., DNA Cell Biol. 10, 1–14 (1991)] in which a nomenclature system, based on divergent evolution of the superfamily, has been described. For the gene and cDNA, we recommend that the italicized root symbol "CYP" for human ("Cyp" for mouse), representing "cytochrome P450," be followed by an Arabic number denoting the family, a letter designating...

https://www.liebertpub.com/doi/pdf/10.1089/dna.1993.12.1

The P450 superfamily: update on new sequences, gene mapping, accession numbers, early trivial names of enzymes, and nomenclature.

Eight different forms of cytochrome P-450 (P-450) were purified to electrophoretic homogeneity by a common procedure from liver microsomes of rats treated with phenobarbital or beta-naphthoflavone. Antibodies were prepared to seven of these forms in rabbits. The eight P-450s were distinguished by spectral properties of the ferric, ferrous, and ferrous carbonyl forms, apparent monomeric molecular weights, peptide mapping, immunological reactivity as discerned by double-diffusion immunoprecipitin analysis and crossed immunoelectrophoresis, and catalytic activities toward the substrates acetanilide, aminopyrine, aniline, benzo[a]-pyrene, d-benzphetamine, N,N-dimethylnitrosamine, 7-ethoxycoumarin, 7-ethoxyresorufin, ethylmorphine, p-nitroanisole, testosterone, and (R)- and (S)-warfarin. Crossed sodium dodecyl sulfate-polyacrylamide gel immunoelectrophoresis was used to estimate the levels of each of the eight forms of P-450 present in the liver microsomes of untreated rats and rats treated with phenobarbital, 5,6-benzoflavone, pregnenolone-16 alpha-carbonitrile, isosafrole, or the polychlorinated biphenyl mixture Aroclor 1254. In each situation, the sum of the levels of these eight P-450s was at least as high as the spectrally determined P-450 content. The results clearly demonstrate that individual forms of P-450 can be induced by different compounds and that a single compound can lower the level of one form of P-450 while inducing one or more other forms of P-450. Catalytic activities toward each of the substrates observed with microsomal preparations are compared to rates predicted on the basis of the content of each of the eight P-450s. These studies provide a basis for further studies on the regulation of individual P-450s, the physical properties of the different P-450s, and the metabolic consequences of changes in the forms of P-450 in rat liver models.

Purification and characterization of liver microsomal cytochromes p-450: electrophoretic, spectral, catalytic, and immunochemical properties and inducibility of eight isozymes isolated from rats treated with phenobarbital or beta-naphthoflavone.

2(3)-tert-Butyl-4-hydroxyanisole (BHA) is one of several widely used antioxidant food additives that protect against chemical carcinogenesis and toxicity. The present report concerns the enhancement of dicoumarol-inhibited NAD(P)H:quinone reductase [NAD(P)H dehydrogenase (quinone); NAD(P)H:(quinone acceptor) oxidoreductase, EC 1.6.99.2] activity in mouse tissues in response to dietary administration of BHA. Cytosolic quinone reductase specific activity was increased significantly in 10 of 15 tissues examined from BHA-fed mice. The greatest proportionate increase, to 10 times control levels, was observed in liver. BHA also increased the quinone reductase activities of kidney, lung, and the mucosa of the upper small intestine severalfold. The increases of quinone reductase activities in liver and digestive tissues in response to BHA were comparable to the increases previously observed in glutathione S-transferase (EC 2.5.1.18) and epoxide hydratase (EC 3.3.2.3) activities. Quinones are among the toxic products of oxidative metabolism of aromatic hydrocarbons. NAD(P)H:quinone reductase exhibits broad specificity for structurally diverse hydrophobic quinones and may facilitate the microsomal metabolism of quinones to readily excreted conjugates. The protective effects of BHA appear to be due, at least in part, to the ability of this antioxidant to increase the activities in rodent tissues of several enzymes involved in the nonoxidative metabolism of a wide variety of xenobiotics.

https://www.pnas.org/content/pnas/77/9/5216.full.pdf

Increase of NAD(P)H:quinone reductase by dietary antioxidants: possible role in protection against carcinogenesis and toxicity

Alcoholic fatty liver: its pathogenesis and mechanism of progression to inflammation and fibrosis

The influence of age, sex, and hormonal status on the expression of eight rat hepatic cytochrome P-450 (P-450) isoenzymes was evaluated by both catalytic and immunochemical methods. The male specificity of P-450 2c(male)/UT-A, the major microsomal steroid 16 alpha-hydroxylase of uninduced rat liver [Waxman, D.J. (1984) J. Biol. Chem. 259, 15481-15490], was shown to reflect its greater than or equal to 30-fold induction at puberty in male but not in female rats. The female specificity of P-450 2d(female)/UT-I was shown to reflect its developmental induction in females. P-450 PB-2a/PCN-E was shown to mediate greater than or equal to 85% of microsomal steroid 6 beta-hydroxylase activity; the male specificity of this P-450 largely reflects its developmental suppression in female rats. Neonatal gonadectomy and hormonal replacement experiments established that neonatal androgen "imprints" or programs the male rat for developmental induction of P-450 2c(male)/UT-A, for maintenance of P-450 PB-2a/PCN-E, and for suppression of P-450 2d(female)/UT-I, all of which occur in male rats at puberty. By contrast, the expressed levels of P-450 isoenzymes PB-1/PB-C, 3/UT-F, PB-4/PB-B, ISF-G, and beta NF-B were mostly unaffected by the rats' age, sex, and hormonal status. Studies on the sex specificity of P-450 induction established that the response of these latter five isoenzymes to the P-450 inducers phenobarbital, beta-naphthoflavone, pregnenolone-16 alpha-carbonitrile, and isosafrole is qualitatively and quantitatively equivalent in females as in males.

Regulation of rat hepatic cytochrome P-450: age-dependent expression, hormonal imprinting, and xenobiotic inducibility of sex-specific isoenzymes

A simple and rapid procedure for the purification of phenobarbitalinducible cytochrome P-450 from rat liver microsomes

The direct oxidation of ethanol by a catalase- and alcohol dehydrogenase-free reconstituted system containing cytochrome P-450☆

Specific antibodies against highly purified cytochrome P450 from phenobarbital (PB)-treated rats and cytochrome P448 from 3-methycholanthrene (MC)-treated rats were produced in rabbits. These antibodies are inhibitors of drug metabolism catalyzed by liver microsomes from untreated rats or from rats treated with PB, MC, or pregnenolone-16α-carbonitrile (PCN). Microsomal metabolism of five substrates was examined; the extent of antibody inhibition was dependent not only on the source of the antibody and microsomes but also on the specific substrate and the reactions catalyzed. A comparison of the antibody inhibition patterns of the various substrates examined indicates a marked difference in the proportions of the different forms of cytochrome P450 present in liver microsomes from untreated and PB-, MC-, and PCN-treated rats. Antibody inhibition of microsomal metabolism indicates that the membrane-bound terminal oxidase, cytochrome P450 or P448, is at least partially exposed to the hydrophilic environment on the exterior of microsomal membranes.

Accessibility of cytochrome P450 in microsomal membranes: inhibition of metabolism by antibodies to cytochrome P450.

Induction of rat liver cytosol methyl red azo-reductase by 3-methylcholanthrene assayed by a sensitive fluorometric method

Publisher Summary This chapter is intended as an overview of the molecular aspects of drug metabolism catalyzed by this hepatic enzyme system. It reviews the recent progress in the isolation and characterization of the protein components constituting this enzyme system, the interaction between these components, and the mechanism of oxygen activation. Cytochrome P450 and NADPH-cytochrome P450 reductase are the two essential protein components of the hepatic microsomal monooxygenase system. Cytochrome P450 is a b-type cytochrome with the protoporphyrin IX prosthetic group. Cytochromes of the b-type are generally characterized by low-spin heme prosthetic groups octahedrally coordinated with the two z-axial positions coordinated to the protein ligands. Although the hepatic microsomal cytochrome P450 system metabolizes compounds at a relatively low rate, it has several other features that make it uniquely suited to oxidizing the non-polar drugs. This enzyme system is able to oxidize and reduce a wide variety of structurally unrelated compounds. The oxidation of medicinal chemicals by the cytochrome P450 containing monooxygenase system is an important initial step in determining the fate of both the chemical agent and the biological system. Metabolism frequently leads to a reduction in the duration of drug action through the formation of less active metabolites and the production of compounds more readily excreted into the urine by the kidneys. This process of metabolic inactivation followed by excretion is the major pathway for terminating the action of a drug in biological systems.

Gerald T. Miwa

Papers

A simple and rapid procedure for the purification of phenobarbitalinducible cytochrome P-450 from rat liver microsomes

The direct oxidation of ethanol by a catalase- and alcohol dehydrogenase-free reconstituted system containing cytochrome P-450☆

Accessibility of cytochrome P450 in microsomal membranes: inhibition of metabolism by antibodies to cytochrome P450.

Induction of rat liver cytosol methyl red azo-reductase by 3-methylcholanthrene assayed by a sensitive fluorometric method

Chapter 22. Molecular Aspects of Drug Metabolism