Enzyme system for the production of signal trunsmitters in human platelets

在胶原激活的人血小板中，胞浆Ca^2+水平的升高不是胶原本身引起的，而是血栓素A_2引起的，血栓素A_2的前体花生四烯酸是通过胶原诱导的肌醇脂代谢产生的。代谢由肌醇脂特异性磷脂酶C、二酰甘油脂酶和单酰甘油脂酶共同催化，从人血小板中纯化了两种特异性磷酸肌醇的胞浆磷脂酶C（PLC）。纯化酶的分子量为440和290 KDa。这些en 2 Ymes分别是同源146 KDa多肽的三聚体和二聚体。146 KDa多肽可能是140-150 KDa PLC同工酶中一种新的免疫学同工酶。这两种酶都以Ca^2+依赖的方式水解磷脂酰肌醇和磷脂酰肌醇-4，5-二磷酸。该酶在无Ca^<2+存在的情况下也能在中性pH下催化反应。

In collagen-activated human platelets, elevation of cytosolic Ca^<2+> 2 level was not caused by collagen itself, but by thromboxane A_2, Of Which precursor arachidonate was produced via collagen-induced inositot lipid metabolism. The metabolism was catalyzed by cooperation of inositol lipid-spercific phospholipase C, diacylglycerol lipase and monoacylglycerol lipase.Two types of cytosolic phospholipase C(PLC) specific for phosphoinositides were purified from human platelets. The molecular masses of the purified en2ymes were 440 ind 290 KDa. These en2Ymes were concluded to be respectively a trimer and a dimer of homologous 146 KDa polypeptides. The 146 KDa polypeptide may be an immunologically novel isozyme among the 140-150 KDa PLC isozymes. Both enzymes hydrolyzed phosphatidylinositol and phosphatidylinositol-4, 5-bisphosphate in a Ca^<2+> 2-dependent manner.Diicylglycerof lipase was partially purified from human platelet membranes. The enzyme catalyzed the reaction around neutral pH even in the absence of Ca^<2+>.Purification and properties of human platelet monoacylglycerof lipase will be examined in near future.