Aggregin and Platelet Aggregation

The platelet surface contains aggregin, a membrane protein with a molecular weight of 100 kDa, which has physical and immunochemical properties that differ from those of platelet glycoprotein Ilia. 

Binding to aggregin is required for epinephrine-induced platelet aggregation to occur. In turn, epinephrine increases the affinity of ADP for its receptor. Thrombin stimulates platelet aggregation independently of ADP, but by raising the level of calcium in the cytoplasm, it activates platelet calpain, which in turn cleaves aggregin. 

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