Abstract
(1) Purification of lipid extracts from human platelets yielded non-lipid material which exhibited anti-thromboplastic and/or anti-thrombic properties. In one instance, both uronic acids and hexosamines were absent; consequently, the anticoagulant activity could not be attributed to the presence of acid mucopolysaccharides. The purified lipid fraction contained most of the thromboplastic activity of human platelets.
(2) The neutral lipid fraction of human platelets contained neither vitamins A, D, E, and K nor steroid hormones. The neutral lipids of human platelets exhibited no thromboplastic activity when tested individually or in combination with one another or with lecithin.
(3) Human platelet phospholipids were resolved into five major fractions by means of silicic acid column chromatography and countercurrent distribution technics. The purified lecithin, sphingomyelin, and inositol phosphatides were void of any thromboplastic activity when tested individually or in combination with one another. It was confirmed that both phosphatidylserine and phosphatidylethanolamine exhibited thromboplastic activity and that phosphatidylserine at high concentrations had a pronounced anticoagulant effect.
(4) When phosphatidylethanolamine and phosphatidylserine were combined, synergistic thromboplastic activity was observed. When phosphatidylserine was combined with lecithin, the thromboplastic activity of phosphatidylserine was greatly enhanced.
