Yamaori Satoshi, Yamazaki Hiroshi, Suzuki Akihiro, Yamada Ayako, Tani Hirofumi, Kamidate Tamio, Fujita Ken ichi, Kamataki Tetsuya
Laboratory of Drug Metabolism, Graduate School of Pharmaceutical Sciences, Hokkaido University, 060-0812 Sapporo, Japan.
Biochem Pharmacol. 2003 Dec 15;66(12):2333-40. doi: 10.1016/j.bcp.2003.08.004.
Effects of cytochrome b(5) (b(5)) on catalytic activities of human cytochrome P450 (CYP) 3A5, CYP3A4, and CYP3A7 coexpressed with human NADPH-cytochrome P450 reductase in Escherichia coli membranes were investigated using 14 substrates. The activities of CYP3A5 were enhanced by addition of b(5) in approximately one third of the substrates employed in this study. Such enhancement by b(5) was roughly similar to that of CYP3A4, while the activities of CYP3A7 were not enhanced by b(5) with any substrates employed. V(max) values for midazolam 1'-hydroxylation and amitriptyline N-demethylation by CYP3A5 were increased about twice by addition of b(5), which was also seen with CYP3A4, although the extent of the effects of b(5) on S(50) (K(m)) and Hill coefficient differed dependent on substrates used. In contrast, b(5) did not alter any of these kinetic parameters of CYP3A7. The effects of b(5) on kinetic parameters of CYP3A5 were similar to those of CYP3A4 but not CYP3A7. These results suggest that roles of b(5) in drug oxidation activities of CYP3A5 and CYP3A4 are different from those of CYP3A7.
利用14种底物研究了细胞色素b(5)（b(5)）对与人NADPH-细胞色素P450还原酶共表达于大肠杆菌膜中的人细胞色素P450（CYP）3A5、CYP3A4和CYP3A7催化活性的影响。在本研究使用的大约三分之一的底物中，添加b(5)可增强CYP3A5的活性。b(5)的这种增强作用与CYP3A4大致相似，而使用任何底物时，b(5)均未增强CYP3A7的活性。添加b(5)后，CYP3A5对咪达唑仑1'-羟基化和阿米替林N-去甲基化的V(max)值增加了约两倍，CYP3A4也出现这种情况，尽管b(5)对S(50)（K(m)）和希尔系数的影响程度因所用底物而异。相比之下，b(5)并未改变CYP3A7的任何这些动力学参数。b(5)对CYP3A5动力学参数的影响与CYP3A4相似，但与CYP3A7不同。这些结果表明，b(5)在CYP3A5和CYP3A4的药物氧化活性中的作用与CYP3A7不同。
