Effect of polylysine on the activation of prothrombin. Polylysine substitutes for calcium ions and factor V in the factor Xa catalyzed activation of prothrombin.

Polylysine has been demonstrated to dramatically accelerate the rate of the factor Xa catalyzed activation of both prothrombin and prethrombin 1. Under the present experimental conditions (pH 8.0, 23 C), no detectable activation of prothrombin or prethrombin 1 occurs with either factor Xa or polylysine alone. The activation of prethrombin 2, the direct precursor of alpha-thrombin, by factor Xa is not stimulated by polylysine. The activation of either prothrombin or prethrombin 1 by factor Xa in the presence of polylysine is partially inhibited by the presence of 5 mM CaCl2. Electrophoretic analysis in sodium dodecyl sulfate showed that the products that were formed in the above activation system comigrated with the reaction products derived from prothrombin activated by factor Xa in the presence of calcium ions and phospholipid. It is suggested that polylysine stimulates the factor Xa-catalyzes activation of prothrombin by replacing the combination of calcium ions and factor V.