Shimada T, Gillam E M, Sutter T R, Strickland P T, Guengerich F P, Yamazaki H
Osaka Prefectural Institute of Public Health, Japan.
Drug Metab Dispos. 1997 May;25(5):617-22.
Human cytochrome P450 (P450) 1B1 (CYP1B1) has recently been shown to be an important enzyme in the activation of diverse procarcinogens such as arylarenes, nitroarenes, and arylamines to reactive metabolites that cause DNA damage in the cells. However, it is not known whether this P450 enzyme also plays roles in the oxidation of certain drugs or model substrates commonly used in P450 assays. We examined the substrate oxidation activities of recombinant human CYP1B1 in yeast microsomes and compared these activities with those catalyzed by reconstituted systems containing recombinant CYP1A1 and CYP1A2 which were isolated from membranes of Escherichia coli in which respective cDNAs have been expressed. Catalytic activities towards some of the model substrates of other human P450 enzymes including CYP2A6, 2C9, 2C19, 2D6, 2E1, and 3A4 were also determined and compared. CYP1B1 catalyzed benzo[a]pyrene 3-hydroxylation at rates lower than those of CYP1A1 but higher than those of CYP1A2. The activity towards 7-ethoxyresorufin O-deethylation catalyzed by CYP1B1 was about one-tenth of that of CYP1A1, but the Km values were lower for CYP1B1 than those for CYP1A1 and CYP1A2. CYP1B1 was also able to catalyze the oxidation of theophylline and caffeine, two prototypic substrates for CYP1A2. CYP1B1 did not oxidize other typical P450 substrates such as coumarin, tolbutamide, S-mephenytoin, chlorzoxazone, nifedipine, and testosterone, while low rates of oxidation of bufuralol and 7-ethoxycoumarin were found for CYP1B1. These results indicate that CYP1B1 has catalytic activities overlapping CYP1A1 and CYP1A2 with respect to the oxidation of drugs and model P450 substrates, although the relative catalytic roles in these three P450 enzymes differ depending upon the substrates examined. A distinct marker activity of CYP1B1 has not been identified.
人类细胞色素P450（P450）1B1（CYP1B1）最近被证明是一种重要的酶，可将多种前致癌物如芳基芳烃、硝基芳烃和芳胺激活为能导致细胞DNA损伤的反应性代谢产物。然而，尚不清楚这种P450酶是否也在某些药物或P450检测中常用的模型底物的氧化过程中发挥作用。我们检测了重组人CYP1B1在酵母微粒体中的底物氧化活性，并将这些活性与含有从表达了各自cDNA的大肠杆菌膜中分离出的重组CYP1A1和CYP1A2的重组系统所催化的活性进行比较。还测定并比较了CYP1B1对包括CYP2A6、2C9、2C19、2D6、2E1和3A4在内的其他人类P450酶的一些模型底物的催化活性。CYP1B1催化苯并[a]芘3-羟基化的速率低于CYP1A1，但高于CYP1A2。CYP1B1催化的7-乙氧基试卤灵O-脱乙基活性约为CYP1A1的十分之一，但CYP1B1的Km值低于CYP1A1和CYP1A2。CYP1B1还能够催化茶碱和咖啡因（CYP1A2的两种典型底物）的氧化。CYP1B1不氧化其他典型的P450底物，如香豆素、甲苯磺丁脲、S-美芬妥因、氯唑沙宗、硝苯地平和睾酮，而CYP1B1对布非洛尔和7-乙氧基香豆素的氧化速率较低。这些结果表明，就药物和模型P450底物的氧化而言，CYP1B1具有与CYP1A1和CYP1A2重叠的催化活性，尽管这三种P450酶在这些底物上的相对催化作用因所检测的底物而异。尚未鉴定出CYP1B1独特的标记活性。
