FUNCTION OF Ac-GLOBULIN AND LIPID IN BLOOD CLOTTING

Abstract

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-globulin, brain thromboplastin, and autoprothrombin I were respectively 500:26:20:400. Generally, lipid is present in lowest concentration and functions nonspecifically. Each lipid, such as brain thromboplastin, platelet factor 3, and crude cephalin, has its own peculiarities. The function of the lipids is in terms of the enzymes that originate from prothrombin itself. As soon as autoprothrombin C-AcG was constituted the full activity was there and was maintained. By contrast, when thrombin-AcG was constituted activity was there at once, tended to increase, and then subsided. Thrombin tends to activate Ac-globulin. The activity measured as Ac-globulin activity is nothing else than accelerated thrombin and (or) autoprothrombin C activity. When thrombin-AcG was used for activating prothrombin to thrombin there was no autoprothrombin C. Instead, there was another activation product called autoprothrombin III. This was isolated as a single component.