The Prothrombin Activator of Echis Carinatus Venom:Characterization and Mode of Action

The venom of the saw scaled viper, Echis carinatus, contains a protein capable of convertis prothrombin to thrombin. This prothrombin activator (ECA) has been purified 45-fold by affinity chromatography on wheat germ agglutinin followed by ion exchange chromatography on DEAE-Sephacil. ECA was homogeneous as assessed by dodecyl sulfate poly acrylamide gel electrophoresis (SDS-PACE). Sialic acid, neutral sugars, and hexosamines were present at 4.2, 7.2 and 5.8 w/wX respectively. Amino acid analysis of reduced and carboxymethylated ECA revealed an unusually high cysteine content of 9 moles %. ECA is inhibited by chelators such as EDTA and o-phenthroline, but is active after treatment with chelex. However, atomic absorption studies revealed that neither Ca, Co, Cr, Cu, FeMηnor घη is present at more than 0.01 moles/mole of active protein after chelex treatment. Arrhenlus plots of the temperature dependence of thrombin formation give a similar activation energy and T½ as Arrhenlus plots of data obtained for a temperature induced conformational change in prothrombin. These data suggest that the activation of prothrombin by ECA requires a particular conformational Isomer of prothrombin as well as a group on ECA which can interact with metal chelators.(Supported, in part, by NIH Grant HL 19282)