ACTIVE-SITE LYSINE BACKBONE UNDERGOES CONFORMATIONAL-CHANGES IN THE BACTERIORHODOPSIN PHOTOCYCLE

Results are presented demonstrating that the backbone of the active si te lysine of bacteriorhodopsin undergoes light-induced structural alte rations during bacteriorhodopsin-mediated light-induced proton pumping . This conclusion is based on difference Fourier transform infrared sp ectroscopy of isotopically labeled bacteriorhodopsin. The data demonst rate that the backbone carbonyl of lysine achieves an extremely low vi brational frequency during M(412) intermediate formation. This is prec eded by a structural transition in the lysine backbone that leads to a n active site lysine carbonyl with the observed low vibrational freque ncy, probably due to a high degree of solvation.