LAMPREY BUT NOT PORCINE INSULIN BINDS WITH DIFFERENT AFFINITY TO LAMPREY AND RAT HEPATOCYTES

The displacement of porcine [I-125] insulin bound to rat and lamprey i solated hepatocytes with unlabeled lamprey and porcine insulins was in vestigated. Binding affinity of lamprey insulin for insulin receptor o f rat was similar to that of porcine insulin. In contrast, the binding affinity of lamprey insulin for its;own insulin receptor was higher t han for a rat receptor. To determine the binding affinity constants of lamprey insulin receptor, the competition binding experiments were ca rried out on isolated lamprey hepatocytes using lamprey insulin as unl abeled ligand and tracer. The affinity of the same binding sites on la mprey hepatocytes was assessed in similar experiments but employing po rcine insulin as unlabeled ligand and tracer. It was found that while Kd of low affinity binding sites on lamprey hepatocytes were similar f or lamprey and porcine insulins, the Kd of high affinity binding sites was different: the displacement curve for lamprey insulin being shift ed to the left as compared to the curve for porcine insulin. The numbe r of high and low affinity binding sites, calculated independently in Scatchard plots, was equal. We conclude that the high affinity insulin binding sites of lamprey but not of rat hepatocytes reveal some speci es specificity in ligand-receptor interaction. (C) 1997 Elsevier Scien ce Inc.