STUDIES ON THE STATE OF INSULIN IN BLOOD: THE STATE AND TRANSPORT OF INSULIN IN BLOOD¹

Abstract

Studies presented in this communication suggest that a major fraction of insulin in blood circulates in a complex form with other substances, more specifically, basic proteins. The basic protein-insulin complex(es) in blood could be adsorbed on cationic exchange resin, in the sodium form, and could be elutcd from the resin by acid or alkali. Control experiments demonstrated that under identical conditions free, crystalline insulin could not be adsorbed on this resin. Blood insulin in its complex form did not exhibit full insulin activity when examined bjr in vitro assays. Full insulin activity could be demonstrated by dissociation of the insulin from its complex(es) either through isoelectric precipitation of the carrier protein(s) or by incubation of the insulin complex(es) with human or rat adipose tissue extracts. The transport of insulin in blood by basic proteins may serve as a regulatory mechanism of insulin activity through the equilibrium between “bound” and “unbound” insulin.