Abstract
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 theKm 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.
Footnotes
-
Send reprint requests to: Dr. T. Shimada, Osaka Prefectural Institute of Public Health, 3–69 Nakamichi 1-chome, Higashinari-ku, Osaka 537, Japan.
-
This work was supported in part by Grants from the Ministry of Education, Science, and Culture of Japan; the Ministry of Health and Welfare of Japan; the Developmental and Creative Studies from Osaka Prefectural Government; and by United States Public Health Service Grants CA44353, ES00267, ES06071, and ES06052.
- Abbreviations used are::
- P450 or CYP
- cytochrome P450
- b5
- cytochromeb5
- IgG
- immunoglobulin G
- HEPES
- N-(2-hydroxyethyl)piperazine-N′-(2-ethanesulfonate)
- Received November 11, 1996.
- Accepted February 17, 1997.
- The American Society for Pharmacology and Experimental Therapeutics
DMD articles become freely available 12 months after publication, and remain freely available for 5 years.Non-open access articles that fall outside this five year window are available only to institutional subscribers and current ASPET members, or through the article purchase feature at the bottom of the page.
|