INHIBITION OF THE M1-]M2 (M-CLOSED-]M-OPEN) TRANSITION IN THE D96N MUTANT PHOTOCYCLE AND ITS RELATION TO THE CORRESPONDING TRANSITION IN WILD-TYPE BACTERIORHODOPSIN

Glutaraldehyde, Iutetium ions and glycerol inhibit the blue shift of t he difference spectra maximum of the M intermediate in the D96N mutant . The M formed has a spectrum indistinguishable from the M intermediat e in wild-type bacteriorhodopsin. It has been concluded that the M-ope n form previously described by us is identical to the M2 and M-n inter mediates postulated by Zimanyi et al. (Photochem. Photobiol. (1992) 56 , 1049-1055) and Sasaki et al. (J. Biol. Chem. (1992) 267, 20782-20786 ), respectively. It is supposed that its formation is accompanied by t he appearance of the cytoplasmic proton half-channel. M-open in the wi ld-type protein is present in a very low amount due to the shift of th e M-closed <-> M-open equilibrium towards the M-closed. The inhibitors used do not prevent the multiphase pattern of the M formation in eith er mutant or wild-type proteins. (C) 1997 Federation of European Bioch emical Societies.