Studies on human platelet granules and membranes.

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Abstract
Homogenates of human platelets were subjected to continuous sucrose gradient ultracentrifugation and separated into granule and membrane components. The effectiveness of the homogenization process and the results of ultracentrifugation were evaluated by electron microscopy. Acid hydrolytic enzyme activity (lysosomal) was associated with the platelet granules. This activity could be increased by treatment with Triton X-100, but not by physical disruption of the granules. The platelet membranes were more efficient as clot-promoting agents than the granules although the degree of effectiveness was variable. The differential was eliminated when the lipids were extracted from the granules and membranes. The lipoprotein of platelet membranes may be more "available" for interaction with coagulation proteins than was the lipoprotein from the granules. Platelet granules are probably primarily concerned with lysosomal and metabolic activities, and the platelet membranes furnish a catalytic surface for the formation of the intrinsic prothrombin activator.