Recognition of human insulin and proinsulin by monoclonal antibodies.

High-affinity monoclonal antibodies (MAB) were obtained from lymph node cell fusions. Affinities ranging from 0.8 X 10(9) L/M to 5.2 X 10(9) L/M were calculated from binding studies with monoiodinated human, bovine, and porcine insulins and human proinsulin. Two monoclonal antibodies were specific for human insulin, recognizing an epitope involving the amino acid B-30 (Thr). Another two monoclonal antibodies were bound to the C-terminal end of the B-chain near B-30. The B-chain-specific monoclonal antibodies did not bind human proinsulin. One monoclonal antibody recognized the A-chain loop in the positions A-8 to A-10. This antibody bound also to human proinsulin. It was concluded that the A-chain loop is exposed on the surface of proinsulin, while the C-terminal B-chain is not available for binding. The study shows that monoclonal antibodies can be used to characterize structures of insulin and proinsulin. In contrast to x-ray studies, the molecules can be used at low concentrations in soluble form. It is suggested to use monoclonal antibodies for the screening of atypical insulins in the serum of diabetic patients and for the further refinement of insulin and proinsulin measurements.