Interaction of insulin with the cell membrane: the primary action of insulin.

Insulin can be covalently attached to a large polymers of Sepharose through the alpha-amino group of the N-terminal residue of the B chain, or through the epsilon-amino group of its lysyl residue. Such derivatives effectively increase the utilization of glucose, and suppress the hormone-stimulated lipolysis, of isolated fat cells. The effects occur with concentrations of insulin-Sepharose that are nearly as low as those of native insulin, and the maximal responses are the same. The results indicate that interaction of insulin with superficial membrane structures alone may suffice to initiate transport as well as other metabolic alterations.