Snake venom. The amino-acid sequence of the subunits of two reduced and S-carboxymethylated proteins (C8S2 and C9S3) from Dendroaspis angusticeps venom.

Two proteins (C8S2 and C9S3) were purified from Dendroaspis angusticeps venom. Whereas protein C8S2 comprises 124 amino acid residues, protein C9S3 contains 125 and each includes 16 half-cystines. After reduction and S-carboxymethylation of the proteins, the subunits were shown to contain 62--63 residues including 8 half-cystine residues. The complete sequences of the subunits have been elucidated. The sequences of the subunits of protein C8S2 and C9S3 are homologous to those of protein S2C4 from D. jamesoni kaimosae. Further, in all the subunits one of the structurally invariant amino acids, Tyr25, has been replaced by phenylalanine or asparagine and the Cys66 occurs in position 57. All the subunits apparently contain only two of the five functionally invariant residues of the neurotoxins, viz. Lys27 and Trp29. Mixtures of proteins S2C4, C8S2, C9S3 and angusticeps-type proteins showed a marked synergistic toxic effect.