COMPARISON OF INHIBITORY EFFECTS ON INTERMEDIATE M-DECAY IN PHOTOCYCLE OF WILD-TYPE BACTERIORHODOPSIN AND D96N MUTANT

Effects of the agents known to decelerate the M intermediate decay in the wild-type bacteriorhodopsin photocycle on the M intermediate decay in the D96N mutant have been studied. Glutaraldehyde or LuCl3 treatme nt of the wild-type and D96N purple membranes results in the appearanc e of two bacteriorhodopsin populations differing in the M intermediate decay rates. In glutaraldehyde-treated wild-type membranes, the M int ermediate decay rates of these populations decrease 10- and 70-fold. L uCl3 decelerates the M decay 150- and 3000-fold. However, neither glut araldehyde nor LuCl3 affect the M decay of these two populations in th e mutant membranes. However, both agents inhibit azide-facilitated dec ay of the M intermediate and shift the linear part of the dose-respons e curve of the effect of the azide concentration on the intermediate M decay rate to higher azide concentrations. The efficiency of azide as an accelerator of the M intermediate decay in these two populations d ecreases 11- and 140-fold in the presence of glutaraldehyde and 200- a nd 1600-fold in the presence of LuCl3. Glycerol and sucrose induce dec eleration of the M intermediate decay in the wild-type bacteriorhodops in and in the D96N mutant in the presence of azide, A scheme for the p hotocycle is suggested that assumes an equilibrium of two M intermedia te forms differing in permeability for azide and, probably, for water molecules.