Structure and function of insulin: preparation and biological activity of guinea pig des B-Asp30,des-A-Asn21-insulin.

Bovine des-B-Ala30,des-A-Asn21-insulin and guinea pig des-B-Asp30,des-A-Asn21-insulin were prepared from bovine and guinea pig insulin by digestion with carboxypeptidase A (EC 3.4.12.2). As reported by other investigators, the biological activity of bovine des-Ala30,des-Asn21-insulin was less than 10% that of bovine insulin. Contrary to theoretical consideration, removal of A-Asn21 and B-Asp30 from the carbosyl termini of guinea pig insulin resulted in a loss of more than 90% of the biological activity. Receptor binding studies of these insulin derivatives demonstrated a good correlation between the loss of biological activity and the decrease in binding affinity. It is suggested that the carboxyl terminal A-Asn21 of insulin may interact directly with the insulin receptor.