FUNCTION OF AC-GLOBULIN AND LIPID IN BLOOD CLOTTING.

In this kinetic study of prothrombin activation prothrombin, thrombin, autoprothrombin C, autoprothrombin I, and Ac-globulin were used in purified form. The lipids used were protein-free sedimentable brain thromboplastin and crude "cephalin". Ac-globulin changed the substrate specificity of autoprothrombin C so that the latter really functions quite as another enzyme designated autoprothrombin C-AcG. The enzyme specificity of thrombin was also changed with Ac-globulin. The modified enzyme is designated thrombin-AcG. The two enzymes from prothrombin function in autocatalysis, and Ac-globulin is a co-autocatalyst. Thrombin-AcG is relatively a weaker enzyme than autoprothrombin C-AcG. With brain thromboplastin and Ac-globulin the two activation products are thrombin and autoprothrombin C. If the two procoagulants, brain thromboplastin and Ac-globulin, are in low concentration, autoprothrombin I compensates for the deficiency. In a typical prothrombin activation the microgram proportions of prothrombin, Ac-gl...