Supernormal insulin: [D-PheB24]-insulin with increased affinity for insulin receptors

D-Phe^B24]- and D-Phe^B25]-human insulin were semisynthesized from porcine insulin by enzyme assisted coupling method. Receptor binding ability of D-Phe^B24]- and D-Phe^B25]-insulin was 180% and 4%, respectively, of that of human insulin. Increased affinity of D-Phe^B24]-insulin was ascribed to markedly decreased dissociation rate in binding to human cultured lymphocytes. Negative cooperative effect of D-Phe^B24]insulin was also increased to twice of that of human insulin. Biological activity of these analogues was assessed by 2-deoxy-glucose uptake studies in isolated adipocytes and the ability of D-Phe^B24]- and D-Phe^B25]-insulin was 140% and 4%, respectively, of that of human insulin. These findings suggest that B25 L-Phe is more crucial for receptor binding and that D-Phe^B24]-insulin is the first semisynthetic insulin to show increased affinity for insulin receptors.