Snake venoms. The amino acid sequences of two proteinase inhibitor homologues from Dendroaspis angusticeps venom.

Toxins C13S1C3 and C13S2C3 from D. angusticeps venom were purified by gel filtration and ion exchange chromatography. Whereas C13S1C3 contains 57 amino acids, C13S2C3 contains 59 but each include six half-cystine residues. The complete primary structure of the low toxicity proteins have been elucidated. The sequences and the invariant residues of toxins C13S1C3 and C13S2C3 from D. angusticeps venom resemble, respectively, those of the proteinase inhibitor homologues K and I from D. polylepis polylepis venom and they are also homologous to the active proteinase inhibitors from various sources. In C13S1C3 and K the active site lysyl residue of active bovine pancreatic proteinase inhibitor is conserved but the site residue alanine, is replaced by lysine. In C13S2C3 and I the active site residue is replaced by tyrosine.