Plasma and platelet fibrinogen differ in gamma chain content

The polypeptide chain composition of fibrinogen and crosslinked fibrin from normal platelets and plasma has been compared by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Fibrinogen was prepared from a lysate of normal human platelets by ethanol precipitation and by antifibrinogen immunoaffinity chromatography. While the A alpha chains of platelet fibrinogen appeared to be somewhat degraded, the electrophoretic mobilities of purified platelet and plasma fibrinogen B beta and gamma chains were the same. Crosslinked fibrin was prepared from platelet and plasma fibrinogen and gamma chain dimers identified by their electrophoretic mobility, incorporation of the lysine analog dansyl cadaverine during crosslinking, and by reaction with antifibrinogen antibody in Western blots. Platelet crosslinked fibrin had a different polypeptide chain composition than that of plasma crosslinked fibrin with absence of the gamma 50-gamma 57.5 dimer in the platelet fibrin. This finding indicates that the gamma 57.5 chain, which constitutes 5% of total normal plasma fibrinogen gamma chains, is either absent or present in markedly reduced amounts in platelet fibrinogen.