AMIDE HYDROGEN-EXCHANGE OF THE CENTRAL B-CHAIN HELIX WITHIN THE T-STATES AND R-STATES OF INSULIN HEXAMERS

Comparative analysis of the H-1-NMR spectra of human insulin shows tha t in the presence of the allosteric ligand, phenol, the tertiary struc ture of the protein is altered as evidenced by the decreased rate of a mide hydrogen-deuterium exchange. In particular, exchange of amide pro tons in residues of the B-chain helix (B-9-B-20) are significantly aff ected suggesting either a stabilization of this helix or a reduction i n the solvent accessibility of the helix in the R-state. This paper ex emplifies the exchange rates of two amides (Val(B18) and Tyr(B16)) fro m this helix which decrease by approximately 400-fold as a result of t his ligand induced conformational transition.