Purification of a protein C activator from the venom of the southern copperhead snake (Agkistrodon contortrix contortrix)

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Abstract
A protease has been purified by ion-exchange chromatography from the venom of Agkistrodon contortrix contortrix (Southern copperhead snake) that can activate the vitamin K dependent protein, protein C. The apparent molecular weight of this protease, determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, was 20000 under nonreducing conditions. Incubation of this protease with plasma resulted in a prolongation of the clotting time and a time-dependent increase in amidolytic activity. Incubation of the protease with purified protein C resulted in an increase in both amidolytic and anticoagulant activity. The protease had no inhibitory effect on thrombin, factor V, fibrinogen, or factor X. It had slight clotting activity toward fibrinogen. The apparent Km of the protease for protein C was 0.28 .mu.M. Calcium ions were observed to inhibit protein C activation with an apparent Ki of 0.2 mM. Ethylenediaminetetraacetic acid, diisopropyl fluorophosphate, and soybean trypsin inhibitor were observed to inhibit the venom protease. These results suggest that the venom of the Southern copperhead snake contains a protease that is a specific activator of protein C.