Inhibition of the protein C activator Protac, a serine proteinase from the venom of the southern copperhead snake Agkistrodon contortrix contortrix.

ProtacR, the single chain glycoprotein in the venom of Agkistrodon contortrix snake subspecies and related pit vipers has found broad application as a protein C activator in blood coagulation research and diagnosis. Inhibition studies were performed to further elucidate the nature of this serine proteinase. Benzamidine derivatives are poor inhibitors of ProtacR. Only a few 4-amidinoanilides of N alpha-substituted omega-phenyl-alpha-aminoalkylcarboxylic acids exert potent inhibitory activities. The active site of ProtacR appears to be accessible only for inhibitors with well-fitting structural features.