Enzyme system for the production of signal trunsmitters in human platelets

在胶原活化的人血小板中，细胞内Ca^<2+ bbb2水平的升高不是由胶原本身引起的，而是由血栓素A_2引起的，其前体花生四烯酸酯是通过胶原诱导的肌脂代谢产生的。代谢是由肌醇脂质特异性磷脂酶C、二酰基甘油脂肪酶和单酰基甘油脂肪酶协同催化的。从人血小板中纯化出两种磷酸肌苷特异性胞质磷脂酶C（PLC）。纯化酶的分子量分别为440和290 KDa。这些en2Ymes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同工酶中免疫学上新的同工酶。这两种酶水解磷脂酰肌醇和磷脂酰肌醇- 4,5 -二磷酸以Ca^<2+ bbb2依赖的方式。脂肪酶二酰甘油部分从人血小板膜中纯化。在没有Ca^<2+>的情况下，该酶也能在中性pH下催化反应。人血小板单酰基甘油脂肪酶的纯化和性质将在不久的将来进行研究。

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.