Reorganization of contractile systems and protein tyrosine phosphorylation in platelet aggregation

Platelet aggregation is accompanied with reorganization of contractile systems. This event involves tyrosine phosphorylation of various proteins. When tyrosine phosphorylation is induced by an intracellular trigger as vanadate, a phosphorylated cytosolic 60 Kd protein acts as a nucleating center on which new actin filaments grow. When aggregation is induced by an extracellular signal as ristocetin, actin filaments of the membrane-associated skeleton and the 60 Kd protein bound to this structure migrate toward the cytosol and only in this soluble state the 60 Kd protein undergoes tyrosine phosphorylation and consequently triggers reorganization of contractile systems.