Chromogenic assay for the prothrombin activator ecarin from the venom of the saw-scaled viper (Echis carinatus)

Ecarin, by limited proteolysis and subsequent autocatalytic reactions, causes the conversion of prothrombin into three products with amidolytic activity: meizothrombin, meizothrombin 1 and α-thrombin. Ecarin action may be abolished by ethylenediaminetetraacetic acid and the activity of α-thrombin can, with a high degree of selectivity, be inhibited by heparin. Thus, ecarin potency may be assayed by measuring the meizothrombin activity generated by ecarin action on human plasma in the presence of heparin. The chromogenic substrate Tosyl-glycyl-l-prolyl-l-arginine-p-nitroanilide (Chromozym® TH) is used in this assay.