Robertson I G, Serabjit-Singh C, Croft J E, Philpot R M
Mol Pharmacol. 1983 Jul;24(1):156-62.
Treatment of rabbits with phenobarbital is followed by increases in the hepatic microsomal concentration of cytochrome P-450, form 5, and in the hepatic microsomal metabolism of aromatic amines to mutagenic products. Inhibition by antibodies to form 5 of the activation of 2-aminoanthracene and 2-aminofluorene demonstrates that these increases are directly related. The extent of the apparent induction of form 5 by phenobarbital is determined from single radial immunodiffusion, immunostaining of form 5 on nitrocellulose sheets containing microsomal proteins transferred from polyacrylamide gels, and the amount of antibody required for 50% of maximal inhibition of activity. The results indicate that phenobarbital increases the hepatic microsomal concentration of cytochrome P-450, form 5, to the same extent that it increases form 5-mediated metabolism of aromatic amines to mutagenic products: 10- to 12-fold. In contrast to the effects of phenobarbital, treatment of rabbits with beta-naphthoflavone decreases the hepatic microsomal concentration of cytochrome P-450, form 5, to less than detectable levels and has little effect on the metabolism of aromatic amines to mutagenic products. Our findings, along with the known effects of phenobarbital on cytochrome P-450, form 2, and the known catalytic activity of cytochrome P-450, form 4, lead to the following conclusions: (a) treatment of rabbits with phenobarbital results in increases in the hepatic microsomal concentrations of at least two structurally, immunochemically, and catalytically distinct isozymes of cytochrome P-450, forms 2 and 5; (b) the metabolism of aromatic amines to mutagenic products in rabbit hepatic microsomal preparations depends on the relative concentrations of at least two isozymes of cytochrome P-450, forms 4 and 5, that change in response to different inducers.
用苯巴比妥处理兔子后，细胞色素P - 450 5型的肝微粒体浓度会升高，同时芳香胺在肝微粒体中代谢为诱变产物的过程也会增强。用针对5型的抗体抑制2 - 氨基蒽和2 - 氨基芴的活化，表明这些升高是直接相关的。通过单向辐射免疫扩散、在含有从聚丙烯酰胺凝胶转移的微粒体蛋白的硝酸纤维素膜上对5型进行免疫染色以及50%最大活性抑制所需的抗体量，来确定苯巴比妥对5型的表观诱导程度。结果表明，苯巴比妥使细胞色素P - 450 5型的肝微粒体浓度升高的程度，与它使5型介导的芳香胺代谢为诱变产物的程度相同：升高10至12倍。与苯巴比妥的作用相反，用β - 萘黄酮处理兔子会使细胞色素P - 450 5型的肝微粒体浓度降至检测不到的水平以下，并且对芳香胺代谢为诱变产物的过程几乎没有影响。我们的研究结果，连同苯巴比妥对细胞色素P - 450 2型的已知作用以及细胞色素P - 450 4型的已知催化活性，得出以下结论：(a) 用苯巴比妥处理兔子会导致肝微粒体中至少两种在结构、免疫化学和催化方面不同的细胞色素P - 450同工酶，即2型和5型的浓度升高；(b) 兔肝微粒体制剂中芳香胺代谢为诱变产物取决于细胞色素P - 450至少两种同工酶，即4型和5型的相对浓度，这些同工酶会因不同诱导剂而发生变化。
