Receptor binding and negative cooperativity of a mutant insulin, [LeuA3]-insulin.

[LeuA3]-insulin, the third mutant insulin, was semisynthesized and was studied for receptor binding and negative cooperative effects. Receptor binding and biological effects of the mutant insulin were 0.3-0.5% of normal, the lowest among three mutant insulins. However, negative cooperative effects of the mutant insulin were almost normal at higher concentration (greater than 10(-6) M). Monoclonal anti-insulin antibody binding studies revealed that carboxyterminal region of B chain was relatively unchanged. These results suggest that N-terminal region of A-chain extending to A3 is important for receptor binding and confirm that A3 does not play an important role for negative cooperativity.