Pyerin W, Wolf C R, Kinzel V, Kübler D, Oesch F
Carcinogenesis. 1983;4(5):573-6. doi: 10.1093/carcin/4.5.573.
Most chemical carcinogens require activation by polysubstrate monooxygenase. The phosphorylation of essential components of this cytochrome P-450 monooxygenase system, isolated from rabbit liver microsomes, cytochrome P-450 (LM2) and cytochrome reductase, was tested using two different protein kinases. One of the kinases, a cyclic AMP-independent phosvitin kinase (kinase P), was inactive in all systems tested. However, the catalytic subunit of a cyclic AMP-dependent protein kinase (kinase C) catalyzed phosphoryl group transfer to both proteins, but to different extents. Cytochrome P-450 was phosphorylated when added as sole component and also when in the presence of P-450 reductase and phosphatidylcholine. In contrast, the weak phosphorylation of P-450 reductase was reduced considerably in a complete reconstituted system containing P-450 and phosphatidylcholine. The inclusion of kinase P did not alter these results which excludes the possibility that these kinases participate in a sequential phosphorylation mechanism. The monooxygenase constituents themselves were without kinase activity. When hepatic microsomes were isolated in presence of the phosphatase inhibitor sodium fluoride no significant change in monooxygenase (7-ethoxycoumarin O-deethylation) activity was observed, whilst after preincubation with either acid or alkaline phosphatase a significant reduction in monooxygenase activity was measured. Thus, cytochrome P-450 (LM2) is phosphorylatable by protein kinase C and the catalytic activity of polysubstrate monooxygenase decreases after preincubation of microsomes with phosphatases.
大多数化学致癌物需要通过多底物单加氧酶激活。使用两种不同的蛋白激酶测试了从兔肝微粒体中分离出的这种细胞色素P - 450单加氧酶系统的关键成分细胞色素P - 450（LM2）和细胞色素还原酶的磷酸化情况。其中一种激酶，即不依赖环磷酸腺苷的磷蛋白激酶（激酶P），在所有测试系统中均无活性。然而，依赖环磷酸腺苷的蛋白激酶（激酶C）的催化亚基催化了磷酸基团向这两种蛋白质的转移，但程度不同。细胞色素P - 450作为唯一成分添加时以及在存在P - 450还原酶和磷脂酰胆碱的情况下都会发生磷酸化。相比之下，在含有P - 450和磷脂酰胆碱的完整重组系统中，P - 450还原酶的微弱磷酸化显著降低。加入激酶P并没有改变这些结果，这排除了这些激酶参与顺序磷酸化机制的可能性。单加氧酶成分本身没有激酶活性。当在磷酸酶抑制剂氟化钠存在下分离肝微粒体时，未观察到单加氧酶（7 - 乙氧基香豆素O - 脱乙基化）活性有显著变化，而在用酸性或碱性磷酸酶预孵育后，单加氧酶活性显著降低。因此，细胞色素P - 450（LM2）可被蛋白激酶C磷酸化，并且微粒体与磷酸酶预孵育后多底物单加氧酶的催化活性降低。
