Romano M C, Eckardt R D, Bender P E, Leonard T B, Straub K M, Newton J F
J Biol Chem. 1987 Feb 5;262(4):1590-5.
omega-Hydroxylation of leukotriene B4 (LTB4) has been reported in human and rodent polymorphonuclear leukocytes; preliminary information indicates that this metabolism is cytochrome P-450 dependent. Therefore, these studies were initiated to characterize the cytochrome P-450-dependent metabolism of LTB4 in other tissues. LTB4 was metabolized by rat hepatic microsomes to two products, 20-hydroxy(omega)-LTB4 and 19-hydroxy(omega-1)-LTB4. The formation of these metabolites was both oxygen and NADPH dependent indicating that a monooxygenase(s) was responsible for these reactions. The apparent Km and Vmax for LTB4 omega-hydroxylase were 40.28 microM and 1202 pmol/min/mg of protein, respectively. In contrast, the apparent Km and Vmax for LTB4 (omega-1)-hydroxylase were 61.52 microM and 73.50 pmol/min/mg of protein, respectively. Both LTB4 omega- and (omega-1)-hydroxylases were inhibited by metyrapone in a concentration-dependent fashion. However, SK&F 525A inhibited LTB4 (omega-1)- but not omega-hydroxylase. In contrast, alpha-naphthoflavone decreased LTB4 omega- but not (omega-1)-hydroxylase activities. The differences in the Km apparent for substrate as well as the differential inhibition by inhibitors of cytochrome P-450 suggest that the omega- and (omega-1)-hydroxylations of LTB4 in hepatic microsomes are mediated by different isozymes of P-450. Furthermore, several additional characteristics of LTB4 hydroxylases indicate that these isozymes of P-450 may be different from those which catalyze similar reactions on medium-chain fatty acids, such as laurate and prostaglandins.
据报道，人类和啮齿动物的多形核白细胞中存在白三烯B4（LTB4）的ω-羟基化作用；初步信息表明这种代谢作用依赖细胞色素P-450。因此，启动了这些研究以表征LTB4在其他组织中依赖细胞色素P-450的代谢作用。LTB4被大鼠肝微粒体代谢为两种产物，即20-羟基（ω）-LTB4和19-羟基（ω-1）-LTB4。这些代谢产物的形成既依赖氧气也依赖NADPH，这表明一种单加氧酶负责这些反应。LTB4 ω-羟化酶的表观Km和Vmax分别为40.28 μM和1202 pmol/分钟/毫克蛋白质。相比之下，LTB4（ω-1）-羟化酶的表观Km和Vmax分别为61.52 μM和73.50 pmol/分钟/毫克蛋白质。LTB4的ω-羟化酶和（ω-1）-羟化酶均被甲吡酮以浓度依赖性方式抑制。然而，SK&F 525A抑制LTB4（ω-1）-羟化酶但不抑制ω-羟化酶。相反，α-萘黄酮降低LTB4 ω-羟化酶的活性但不降低（ω-1）-羟化酶的活性。底物的表观Km差异以及细胞色素P-450抑制剂的差异抑制作用表明，肝微粒体中LTB4的ω-羟基化和（ω-1）-羟基化是由不同的P-450同工酶介导的。此外，LTB4羟化酶的几个其他特征表明，这些P-450同工酶可能不同于那些催化中链脂肪酸（如月桂酸和前列腺素）类似反应的同工酶。
