Changes in Immunospecificity and Biologic Activity of Bovine Insulin Due to Subsequent Removal of the Amino Acids B1, B2 and B3

Abstract

The influence of splitting off the N-terminal amino acids B1, B2 and B3 of bovine insulin on the binding of these derivatives to antibodies raised with bovine insulin in guinea pigs and on biologic insulin activities is investigated. In comparison with bovine insulin the standard free energies −ΔF°1 for complex formation between high affinity antibodies Ak1 and des-PheB1-insulin or des-(Phe-Val)B1-2-insulin are reduced to 77 per cent and 76.3 per cent respectively, with a further decrease to 68 per cent for des-(Phe-Val-Asn)B1-3-[PyrB4] insulin. The standard free energy -ΔF°2 for complex formation between low affinity antibodies Ak2 and des-PheB1-insulin drops to 48.4 per cent. Further splitting off of the N-terminal amino acids B2 and B3 completely abolishes the antigen binding to Ak2. The ability of both des-PheB1-insulin and des-(Phe-Val)B1-2-insulin to lower the in vivo blood sugar level does not differ significantly from bovine insulin, whereas the in vivo activity of des-(Phe-Val-Asn)B1-3-[PyrB4] insulin decreases to 70±7 per cent. The in vitro biologic activity, tested on isolated fat cells, is slightly reduced to 89±9 per cent for des-PheB1-insulin, to 86±3 per cent for des-(Phe-Val)B1-2-insulin and to 68±6 per cent for des-(Phe-Val-Asn) B1-3-[PyrB4] insulin.