Characterization of three fibrinogenolytic proteases isolated from the venom of Taiwan habu (Trimeresurus mucrosquamatus).

Snake venoms, particularly those belonging to Crotalidae and Viperidae families, are known to possess fibrinogenolytic proteases which strongly affect the blood coagulation system. Three fibrinogenolytic enzymes, named as TM-1, TM-2 and TM-3, were purified from the venom of Taiwan habu using anion-exchange and gel-filtration chromatographies followed by cation-exchange HPLC. These enzyme fractions were shown to be homogeneous as judged by SDS-gel electrophoresis. Further characterization of these purified fractions with fibrinogenase activity indicated that they are single-chain proteases possessing basic isoelectric points and molecular masses of approximately 27 kDa. These enzymes cleaved alpha-chain of fibrinogen first and then beta-chain, with relatively low activity on gamma-chain. Fibrinogenolytic activities of these enzymes were not significantly affected at extreme pH values, activity loss occurred only at temperatures higher than 65 degrees C. Enzyme activities were strongly inhibited by some metal chelators such as EDTA or 1,10-phenanthroline, suggesting that these fibrinogenases belong to metalloproteases. The closely similar amino-acid compositions coupled with identical cleaved products of similar molecular masses observed on the autolysis of TM-1 and TM-2 suggest that these two proteases are similar in primary structures and probably mutually related.