Zuber M X, Simpson E R, Waterman M R
Science. 1986 Dec 5;234(4781):1258-61. doi: 10.1126/science.3535074.
Cortisol production requires the activity of only 17 alpha-hydroxylase, whereas the formation of sex steroids requires both 17 alpha-hydroxylase and 17,20-lyase activities. Studies in reconstituted enzyme systems have suggested that a single steroid hydroxylase, 17 alpha-hydroxylase cytochrome P-450 (P-450(17) alpha), catalyzes both activities. By expression of bovine adrenocortical P-450(17 alpha) in COS 1 (transformed monkey kidney) cells, which normally contain no detectable P-450(17) alpha, it has now been established in situ that a single polypeptide chain does catalyze both the 17 alpha-hydroxylase and the 17,20-lyase reactions. This heterologous system supports 17 alpha-hydroxylation of pregnenolone and progesterone with equal efficiency, but catalyzes about five times as much 17,20-lyase activity when 17 alpha-hydroxypregnenolone is the substrate than when 17 alpha-hydroxyprogesterone is the substrate. For these activities to be observed in COS 1 cells, newly synthesized apocytochrome P-450(17) alpha must bind heme and insert into the endoplasmic reticulum such that endogenous cytochrome P-450 reductase can support hydroxylation. Thus, COS 1 cells are a useful system for expression and study of various forms of cytochrome P-450.
皮质醇的生成仅需要17α-羟化酶的活性，而性类固醇的形成则需要17α-羟化酶和17,20-裂解酶的活性。在重组酶系统中的研究表明，单一的类固醇羟化酶，即17α-羟化酶细胞色素P-450（P-450(17)α），催化这两种活性。通过在COS 1（转化的猴肾）细胞中表达牛肾上腺皮质P-450(17α)，该细胞通常不含有可检测到的P-450(17)α，现已在原位确定单一多肽链确实催化17α-羟化酶和17,20-裂解酶反应。这个异源系统以相同的效率支持孕烯醇酮和孕酮的17α-羟化，但当以17α-羟孕烯醇酮为底物时，其催化的17,20-裂解酶活性是17α-羟孕酮为底物时的约五倍。为了在COS 1细胞中观察到这些活性，新合成的脱辅基细胞色素P-450(17)α必须结合血红素并插入内质网，以便内源性细胞色素P-450还原酶能够支持羟化作用。因此，COS 1细胞是用于表达和研究各种形式细胞色素P-450的有用系统。
