CONFORMATIONAL ALTERATIONS OF BOVINE INSULIN ADSORBED ON A SILVER ELECTRODE

Surface enhanced Raman spectra of bovine insulin, adsorbed on the silv er electrode from aqueous solutions of micromolar concentrations, are presented for the potential range -0.2 to -1.2 V/AgCl. The data sugges t that insulin is bound to silver through ionized tyrosine residues an d carboxy terminal groupings. Disulfide linkages are reduced sequentia lly upon increasing negative potential: A7-B7 at -0.3 to -0.5 V, and A 20-B19 at -0.5 to -0.6 V. Rupture of disulfide bonds increases the por tion of beta/disordered conformation at the expense of the alpha helix .