Studies on platelet proteins: IX. The identity of fibrinogen

Abstract

The molecular differences between human platelet fibrinogen and plasma fibrinogen observed previously were further investigated to determine whether the platelet protein might be a proteolytic derivative of its plasma counterpart. Purified plasma fibrinogen labeled with 125I was added to washed, intact platelets, and the total fibrinogen was isolated in the presence of proteolytic inhibitors by the same procedure used for platelet fibrinogen alone. Comparison of control 125I-labeled plasma fibrinogen, total fibrinogen, and platelet fibrinogen by sodium dodecylsulfate gel electrophoretic staining patterns, as well as the radioactivity distribution for control and total fibrinogen, showed no conversion of the added plasma fibrinogen to platelet fibrinogen. Furthermore, the electrophoretic pattern of platelet fibrinogen was different from the slowly clottable plasmin derivative of plasma fibrinogen, termed Fragment X. It is concluded that platelet fibrinogen is not derived, during the course of its isolation, from plasma fibrinogen.