Enzyme studies on human blood; interrelation of heparin and fibrinogen fractions.

I NVESTIGATIONS on the possible mechanism of the anticoagulant action of heparin have centered largely on the problem of its cofactor. In 1918, Howell and Holt (I) showed that heparin requires a blood factor to prevent the coagulation of fibrinogen by thrombin. Subsequently Quick (2) suggested that an albumin fraction contains normal antithrombin, which together with heparin, exerts a powerful anticoagulant action. Others (3,4, 5) confirmed that the heparin cofactor is a substance associated with an albumin fraction, but not crystalline albumin. In a previous communication from this laboratory (6) it was demonstrated that human plasma albumin actually accelerates the reaction of fibrinogen fractions with thrombin. Therefore, in view of this nnding and the reported synergism of antithrombin and heparin, experiments on the influence of heparin on fibrinogen fractions were undertaken.