Abstract
On the membrane surface of the human platelet, phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were hydrolyzed to different extents by the snake venom phospholipases A 2 of varying p I values. The susceptibility of platelet phospholipids to basic phospholipase A 2 of Naja nigricollis (p I 10.6) has been reported (Wang et al. (1986) Biochim. Biophys. Acta 856, 244–258). The susceptibilities of platelet phospholipids to acidic phospholipase A 2 of Naja naja atra (p I 5.2) and to neutral phospholipase A 2 of Hemachatus haemachatus (p I 7.3) were investigated in this study. In gel-filtered platelets, acidic phospholipase A 2 hydrolyzed 35% PC and 10% PE, while neutral phospholipase A 2 hydrolyzed 18% PC and 3% PE. In thrombin-induced shape-changed platelets, acidic phospholipase A 2 hydrolyzed 20% PC and 10% PE, while neutral phospholipase A 2 hydrolyzed 15% PC and 6% PE. In thrombin-activated platelets, acidic phospholipase A 2 hydrolyzed 25% PC and 7% PE, while neutral phospholipase A 2 hydrolyzed 25% PC and 10% PE. Sequential lipid hydrolysis experiments showed that basic phospholipase A 2 of Naja nigricollis could hydrolyze the remaining PC and PE in the membrane previously treated with the neutral enzyme. The results may mean that: (1) the PC and the PE domains exist on the platelet membrane surface; and (2) the lipid domains on the membrane surface of resting platelets are rearranged by thrombin.
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