Partial and selective inactivation of thrombokinase by chymotrypsin.

Thrombokinase has been isolated from bovine plasma in a form that approached electrophoretic homogeneity` and gave a single boundary in the ultracentrifuge.' Such material has four separately measurable activities: 1. activation of prothrombin in the presence of oxalate; 2. activation of prothrombin in the presence of ionic calcium, phospholipid and factor V; 3. activation of chymotrypsinogen; and 4. hydrolysis of tosylarginine methyl ester. The defining property has been taken as the direct, unaided activation of prothrombin, which can be assayed, with thrombokinase. in microgram concentrations. However, thrombokinase can be assayed in nanogram concentrations, provided that the prothrombin is accompanied by ionic calcium, phospholipid and factor V. It is this latter property which has now been preferentially destroyed by chymotrypsin. Moreover, this has been accompanied by a molecular change in the thrombokinase. Such selective inactivation has not heretofore been described for thrombokinase, or for apparently equivalent factors, such as activated factor X and autoprothrombin C. However, a similar molecular variant has now also been found in some preparations of thrombokinase to which no chymotrypsin had been added.