Studies on Human Platelet Gangliosides

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Abstract
Gangliosides, glycosphingolipids which contain sialic acid, were studied in human platelets. They represented 0.5% of the platelet lipids and accounted for 6% of the total neuraminic acid content of platelets. Three major ganglioside fractions were identified and characterized. Ganglioside I was hematoside (G6) and comprised 92% of the platelet gangliosides. It contained glucose, galactose, and sialic acid in molar ratios of 1:1:1 and no hexosamine. The major fatty acid was behenate (22:0). Ganglioside I was also identified in isolated platelet granules and membranes. Ganglioside II (5%) contained glucose, galactose, sialic acid, and hexosamines (molar ratios 1:2:1:1). The hexosamines were glucosamine (72%) and galactosamine (28%). It was therefore designated as ganglioside lacto-N-neotetraose. Ganglioside III (2%) contained disialosyllactosyl ceramide (G3A) as well as two other gangliosides which could not be precisely characterized. Gangliosides I, II, and III were susceptible to the action of Clostridium perfringens neuraminidase as evidenced by full recovery of sialic acid in its free form after incubation. Neutral platelet glycolipids were qualitatively examined by thin-layer chromatography. The major component was lactosyl ceramide. Interactions of gangliosides I and III and serotonin-14C were examined in an equilibrium dialysis system at 4°C. The gangliosides bound serotonin-14C in relatively small quantities, whereas control lipids were negative. The binding was essentially unchanged by reverse dialysis, ultracentrifugation and subsequent thin-layer chromatography. The results are comparable to the previously observed nonmetabolic interactions between whole platelets and serotonin in the cold. It is suggested that the orientation and specific distribution of platelet membrane glycolipids may be important determinants of the unique surface properties of platelets.