Molecular cloning andsequenceanalysis ofthecDNAforancrod, a thrombin-like enzymefrom thevenomofCalloselasma rhodostoma

The1.54 kbcDNA forancrod, a thrombin-like enzyme,was cloned froma AZAPcDNA library derived fromthevenom glands ofCalloselasma (Agkistrodon) rhodostoma. ThecDNA sequencereveals that ancrod issynthesized asa pre-zymogenof 258aminoacids, including a putative secretory peptide of18 aminoacids anda proposed zymogen peptide of6amino-acid residues. Theamino-acid sequenceofthepredicted active form oftheenzyme exhibits a highdegree ofsequencesimilarity to those ofmammalian serine proteases (trypsin andpancreatic kallikrein) andother thrombin-like enzymes (batroxobin and