Enhanced Binding Affinity of Chicken Insulin in Rat Liver Membranes and Human Lymphocytes: Relationship to the Kinetic Properties of the Hormone-Receptor Interaction

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Abstract
The binding of chicken and porcine insulins to rat liver plasma membranes was compared in steady-state and rate experiments. At steadystate, the two insulins reacted with the same complement of receptor sites, but the binding affinity of chicken insulin was about twice as high as that of porcine insulin. The chicken [125I]iodo-insulinreceptor complex dissociated at a slower rate (t½ ≌ 26 min at 30 C) than the porcine [125I]iodo-insulin- receptor complex (t½ ≌ 12 min at 30 C). Similar results, i.e., a slower dissociation rate for chicken [125I]iodo-insulin than for porcine [125I]iodo-insulin were observed also in human cultured lymphocytes, whether dissociation of [125I]iodo-insulin was studied by dilution only or by dilution plus addition of unlabeled (both homologous and heterologous) insulin. In rat liver plasma membranes, the initial rates of binding of both insulins at 20 C or 30 C were similarly dependent on the hormone concentration, regardless of the degree of receptor site-occupancy, and did not appear to differ very greatly. The data suggest that the higher binding affinity and biological potency of chicken insulin, as compared to porcine insulin, can be accounted for mainly by a slower dissociation rate of the chicken insulinreceptor complex.

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