Mori H, Morikawa S, Taniguchi S, Fujii K, Fujiwara M, Fujiwara M, Hosaka K
Department of Pharmacology, Faculty of Medicine, Kyoto University, Japan.
Biochim Biophys Acta. 1989 May 15;1003(1):98-107. doi: 10.1016/0005-2760(89)90105-7.
Endogenous substrates (phosphatidylserine, phosphatidylethanolamine and phosphatidylcholine) for the Ca2+-dependent base-exchange reaction were investigated using bovine retinal microsomes. The amounts of the three bases, serine, ethanolamine and choline, released from the membranes and the amount of phosphatidic acid generated in the membranes were measured in the presence of Ca2+ with or without exogenous bases. When the membranes were incubated with Ca2+ alone, the three bases were liberated into the water-soluble fractions accompanied by accumulation of phosphatidic acid, suggesting the presence of Ca2+-dependent phospholipase D-like activity. When an exogenous base was added to the reaction mixture, the liberation of the other two bases increased slightly and the formation of phosphatidic acid decreased markedly. The exogenous base also stimulated the liberation of the same base from prelabeled phospholipids. Accompanying these changes, the exogenous base was incorporated into the membrane phospholipid. With respect to pH profile, time course and metal requirements, both the base incorporation and phospholipase D-like activity were quite similar. The amount of base incorporated generally agreed with both the decreased amount of phosphatidic acid formed and the increased amount of base released. These results suggest that, beside the base-exchange reaction, phospholipase D-like activity plays an important role in Ca2+-dependent base incorporation into bovine retinal membranes.
利用牛视网膜微粒体研究了Ca2+依赖的碱基交换反应的内源性底物（磷脂酰丝氨酸、磷脂酰乙醇胺和磷脂酰胆碱）。在有或没有外源碱基存在的情况下，在Ca2+存在下测量了从膜中释放的三种碱基（丝氨酸、乙醇胺和胆碱）的量以及膜中产生的磷脂酸的量。当仅用Ca2+孵育膜时，三种碱基释放到水溶性部分，同时伴有磷脂酸的积累，这表明存在Ca2+依赖的磷脂酶D样活性。当向反应混合物中加入外源碱基时，另外两种碱基的释放略有增加，而磷脂酸的形成明显减少。外源碱基还刺激了预标记磷脂中相同碱基的释放。伴随着这些变化，外源碱基被掺入膜磷脂中。关于pH曲线、时间进程和金属需求，碱基掺入和磷脂酶D样活性都非常相似。掺入的碱基数通常与形成的磷脂酸减少量和释放的碱基增加量一致。这些结果表明，除了碱基交换反应外，磷脂酶D样活性在Ca2+依赖的碱基掺入牛视网膜膜中起着重要作用。
