QUANTITATIVE CONCEPTS RELATED TO PROTHROMBIN AND AUTOPROTHROMBIN I ACTIVITY

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Abstract
Russell viper venom can be combined with autoprothrombin I and Ca ions for the activation of purified prothrombin to thrombin provided a small amount of Ac-globulin is also in the reaction mixture. This observation was utilized for developing a quantitative assay for autoprothrombin I concentration. Conditions are arranged so that the yield of thrombin from a purified prothrombin substrate is quantitatively related to the amount of autoprothrombin I in the reaction mixture. Normal human plasma contains about 21 units of autoprothrombin I, and serum contains about 39 units. About 8% of the prothrombin of plasma is converted to autoprothrombin I when blood clots in a test tube. By addition of purified platelet factor 3 to freshly drawn blood, the conversion of prothrombin to autoprothrombin I may involve more than 2/3 of the prothrombin; and, by addition of thromboplastin to freshly drawn blood, about 50% of the prothrombin can be converted to autoprothrombin L It is estimated that the autoprothrombin I concentration of plasma is from 1 to 1.5 mg %.
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