Action of a cysteine proteinase from pupae of the blowfly Aldrichina grahami on the oxidized B-chain of bovine insulin.

A cysteine proteinase purified from pupae of the blowfly (A. grahami) was tested for its peptide-bond specificity against the oxidized B-chain of insulin. Fifteen peptides were separated on HPLC using both gradient and isocratic elution methods. Analyses of amino acid content and N-terminal amino acids indicated that these were eleven homogeneous peptides produced by digestion and undigested insulin B-chain. Glu13-Ala14 and Tyr26-Thr27 were the major cleavage sites, and Asn3-Gln4, Cys7-Gly8, Tyr16-Leu17, Leu17-Val18 and Cys19-Gly20 were also often cleaved. These findings show the similarity between this enzyme and cathepsin L.