The binding of cyclic adenosine 3',5' monophosphate to the insulin hexamer.

Evidence is presented for the binding of cyclic adenosine 3', 5' monophosphate (cAMP) to the insulin hexamer. Addition of cAMP to the T-6 and R(6) insulin hexamers, two allosteric forms of the hexamer, alters significantly the H-1 NMR spectra of three aromatic residues that are located close to the surface of the insulin hexamer, indicating an interaction between the aromatic rings of cAMP and the protons of the insulin residues. The binding of cAMP to the insulin hexamer has never been documented, though cAMP is known to regulate secretion of insulin. This binding may have a role in the regulation of the function of the insulin hexamer in vivo, since the hexamer seem to have a specific binding site for cAMP.