Studies with Tritiated Polypeptide Hormones

Tritiated acetamidino derivatives of insulin are readily prepared. That the reaction is specific for amino groups has been confirmed and the mildest conditions for optimal labeling established. At acid pH, there is no significant loss of tritium from the polypeptide. A small loss of 3H occurs after 3 months at pH 9. Acetamidino-insulin is fully potent in the following assays: mouse convulsion, muscle sugar transport, fat cell glucose oxidation, and immunoassay. A slight loss of potency was observed in some cases with high specific activity preparations. Acetamidination introduces some heterogeneity into insulin preparations, but the products appear to be biologically active and can be separated by disc gel electrophoresis.