Hagfish insulin: the discrepancy between binding affinity and biologic activity.

Hagfish insulin exhibits a binding affinity of about 25% of that of pig insulin in rat adipocytes and IM-9 lymphocytes, even though its relative biologic potency is only about 5% in adipocytes. The dissociation rate constant of hagfish insulin is about half that of pig insulin, and the association rate constant is about one eighth. A longer time is, therefore, required for hagfish insulin to reach a steady state of binding. Failure to reach steady state is the probable reason why some previous results suggested a relative binding affinity of hagfish insulin of the same magnitude as the relative biologic potency.