Wrighton S A, Schuetz E G, Watkins P B, Maurel P, Barwick J, Bailey B S, Hartle H T, Young B, Guzelian P
Mol Pharmacol. 1985 Sep;28(3):312-21.
We have recently demonstrated that P-450p, a form of rat liver cytochrome P-450 inducible by steroids such as dexamethasone and pregnenolone-16 alpha-carbonitrile, by the macrolide antibiotic triacetyloleandomycin, and by phenobarbital, is immunochemically related to and shares 73% NH2-terminal amino acid sequence homology with rabbit cytochrome LM3c. Extending this interspecies comparison we now report that liver microsomes prepared from the rabbit, hamster, gerbil, and mouse contain inducible cytochromes P-450 that resemble P-450p in: (a) converting triacetyloleandomycin to a metabolite that forms a distinct spectral complex with cytochrome P-450 heme, (b) catalyzing the demethylation of erythromycin, and (c) reacting on immunoblots with antibodies directed against P-450p or LM3c. These three characteristics changed in parallel within treatment groups of a given species receiving different inducers of cytochrome P-450. However, there were striking qualitative and quantitative interspecies differences in the responses to inducers. For example, rifampicin was the most efficacious inducer of LM3c in the rabbit and yet was not at all an inducer of P-450p in the rat whereas pregnenolone-16 alpha-carbonitrile, an inducer in the rat, failed to induce LM3c in the rabbit. Immunoblot analysis of these microsomes revealed in each species except the rabbit a single immunochemically related protein. A second immunoreactive protein was present in microsomes from male and female and rifampicin- and dexamethasone-treated female rabbits. Two cloned cDNAs, which hybridized to a species of liver mRNA directing the synthesis of P-450p in a cell-free translation system, were used to probe Northern blots of liver RNAs. These revealed a single band of hybridizable mRNA in each species (except RNA from the rabbit which gave no signal even under conditions of reduced stringency) that was induced in qualitative proportions to that of the accumulated immunoreactive protein. We conclude that P-450p appears to be conserved in evolution and is represented in each of the species tested by one or more immunochemically related proteins which exhibit similar catalytic activities to those of P-450p.
我们最近证实，P-450p是大鼠肝脏细胞色素P-450的一种形式，可被地塞米松和孕烯醇酮-16α-腈等类固醇、大环内酯类抗生素三乙酰竹桃霉素以及苯巴比妥诱导，它与兔细胞色素LM3c在免疫化学上相关，并且在氨基末端氨基酸序列上有73%的同源性。扩展这种种间比较，我们现在报告，从兔、仓鼠、沙鼠和小鼠制备的肝微粒体含有可诱导的细胞色素P-450，它们在以下方面与P-450p相似：（a）将三乙酰竹桃霉素转化为一种与细胞色素P-450血红素形成独特光谱复合物的代谢物，（b）催化红霉素的去甲基化，以及（c）在免疫印迹上与针对P-450p或LM3c的抗体发生反应。在接受不同细胞色素P-450诱导剂的给定物种的治疗组中，这三个特征平行变化。然而，对诱导剂的反应存在显著的种间定性和定量差异。例如，利福平是兔中LM3c最有效的诱导剂，但在大鼠中根本不是P-450p的诱导剂，而孕烯醇酮-16α-腈在大鼠中是诱导剂，在兔中却不能诱导LM3c。对这些微粒体的免疫印迹分析显示，除兔外，每个物种中都有一种免疫化学相关的单一蛋白质。在雄性和雌性以及利福平和地塞米松处理的雌性兔的微粒体中存在第二种免疫反应性蛋白质。两个克隆的cDNA，它们在无细胞翻译系统中与一种指导P-450p合成的肝脏mRNA物种杂交，被用于探测肝脏RNA的Northern印迹。这些结果显示，每个物种中都有一条可杂交的mRNA条带（兔的RNA除外，即使在低严谨度条件下也没有信号），其诱导的定性比例与积累的免疫反应性蛋白质相当。我们得出结论，P-450p在进化中似乎是保守的，并且在每个测试物种中由一种或多种免疫化学相关的蛋白质代表，这些蛋白质表现出与P-450p相似的催化活性。
