Degradation, Receptor Binding Affinity and Biological Potency of Monoiodoinsulin in Isolated Rat Fat Cells

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Abstract
The degradation, binding affinity and biological potency of monoiodoinsulin was studied in isolated rat fat cells. The rate of inactivation by a concentrated cell suspension was indistinguishable from that of native insulin, whereas the relative biological potency (increase in lipid synthesis from glucose) and binding affinity (inhibition of receptor binding of 125I-labelled insulin) was 60-80%. Assuming that the insulin receptor binding is a simple, reversible, bimolecular reaction, the following are the consequences for the interpretation of experiments at equilibrium in which an unlabeled species of insulin competes with (125I) monoiodoinsulin present in a concentration much below the dissociation constant for the insulin: 1. The dissociation constant is estimated without bias. 2. The total number of receptors is slightly underestimated.