Action of human pepsins 1,2,3 and 5 on the oxidized B-chain of insulin.
Human pepsins 1 and 2 attack the B-chain of oxidized insulin at pH 1.7 at the same bonds as does human pepsin 3. At pH 3.5, pepsins 1 and 2 attack insulin B-chain at essentially the same bonds as at pH 1.7, but more slowly. For all three enzymes, the first bond to be hydrolysed is Phe(25)-Tyr(26), followed simultaneously by Glu(13)-Ala(14), Leu(15)-Tyr(16) and Tyr(16)-Leu(17). Human pepsin 5, however, attacks Phe(24)-Phe(25) first of all, followed by Leu(15)-Tyr(16) and Tyr(16)-Leu(17). The results suggest that each pepsin has only one active site. Acid hydrolysis indicates that the sites of enzymic cleavage are not bonds with an inherent instability at low pH.
D000595:Amino Acid Sequence; D001665:Binding Sites; D002854:Chromatography, Paper; D006801:Humans; D007328:Insulin; D010084:Oxidation-Reduction; D010434:Pepsin A; D010446:Peptide Fragments / Q000032:analysis
D007328:Insulin; D010446:Peptide Fragments; D010434:Pepsin A