Tassaneeyakul W, Birkett D J, Veronese M E, McManus M E, Tukey R H, Quattrochi L C, Gelboin H V, Miners J O
Department of Clinical Pharmacology, Flinders Medical Centre, Adelaide, Australia.
J Pharmacol Exp Ther. 1993 Apr;265(1):401-7.
Kinetic and inhibitor studies using cDNA-expressed enzymes and human liver microsomes have characterized the specificity of a range of cytochrome P450 (CYP) 1A substrate and inhibitor probes towards the two isoforms comprising this subfamily. Expressed CYP1A1 and CYP1A2 both catalyzed the O-deethylation of phenacetin, although the apparent Km was about 4-fold lower for CYP1A2 (25 vs. 108 microM). Phenacetin O-deethylation exhibited biphasic kinetics in human liver microsomes, and the apparent Km for the high-affinity component (9 +/- 6 microM) was consistent with the involvement of CYP1A2 in this reaction. The prototypic CYP1A xenobiotic inhibitor and substrate probes alpha-naphthoflavone, ellipticine, 7-ethoxycoumarin and 7-ethoxyresorufin all inhibited CYP1A1- and CYP1A2-mediated phenacetin O-deethylation as well as the high-affinity component of human liver phenacetin O-deethylase activity. alpha-Naphthoflavone and 7-ethoxycoumarin were, however, approximately 10-fold more potent as inhibitors of CYP1A2 than CYP1A1. Other putative human CYP1A xenobiotic substrates and inhibitors, including caffeine, 5- and 8-methoxypsoralen, nifedipine, paraxanthine, propranolol and theophylline similarly inhibited CYP1A1- and 1A2-catalyzed phenacetin O-deethylation and the high-affinity human liver phenacetin O-deethylase. In contrast, the monoclonal antibody MAb 1-7-1, raised against 3-methylcholanthrene-inducible rat cytochromes 450, almost abolished CYP1A1-mediated phenacetin O-deethylation, but had no effect on human liver microsomal- or CYP1A2-catalyzed phenacetin dealkylation. Together with previous data, the results indicate that the majority of human CYP1A xenobiotic inhibitor and substrate probes are nonspecific in their recognition of CYP1A1 and CYP1A2, although selectivity is apparent for some compounds.
利用cDNA表达的酶和人肝微粒体进行的动力学和抑制剂研究，已确定了一系列细胞色素P450（CYP）1A底物和抑制剂探针针对构成该亚家族的两种同工型的特异性。表达的CYP1A1和CYP1A2均催化非那西丁的O-脱乙基反应，尽管CYP1A2的表观Km约低4倍（25对108 microM）。非那西丁O-脱乙基反应在人肝微粒体中表现出双相动力学，高亲和力组分的表观Km（9±6 microM）与CYP1A2参与该反应一致。典型的CYP1A异生物质抑制剂和底物探针α-萘黄酮、玫瑰树碱、7-乙氧基香豆素和7-乙氧基试卤灵均抑制CYP1A1和CYP1A2介导的非那西丁O-脱乙基反应以及人肝非那西丁O-脱乙基酶活性的高亲和力组分。然而，α-萘黄酮和7-乙氧基香豆素作为CYP1A2的抑制剂比CYP1A1强约10倍。其他假定的人CYP1A异生物质底物和抑制剂，包括咖啡因、5-和8-甲氧基补骨脂素、硝苯地平、对黄嘌呤、普萘洛尔和茶碱，同样抑制CYP1A1和1A2催化的非那西丁O-脱乙基反应以及人肝非那西丁高亲和力O-脱乙基酶。相比之下，针对3-甲基胆蒽诱导的大鼠细胞色素450产生的单克隆抗体MAb 1-7-1几乎消除了CYP1A1介导的非那西丁O-脱乙基反应，但对人肝微粒体或CYP1A2催化的非那西丁脱烷基反应没有影响。与先前的数据一起，结果表明，大多数人CYP1A异生物质抑制剂和底物探针在识别CYP1A1和CYP1A2时是非特异性的，尽管某些化合物具有明显的选择性。
