Complicated character of the M decay pH dependence in the D96N mutant is due to the two pathways of the M conversion.
At high ionic strength, the pH dependence of the M intermediate decay in a photocycle of the D96N mutant bacteriorhodopsin shows a complicated behavior which is found to be due to the coexistence of two pathways of the M conversion. The M decay which dominates at pH < 5 is coupled to the proton uptake from the cytoplasmic surface and proceeds probably through the N intermediate. This pathway is inhibited by glutaraldehyde, the potent inhibitor of M decay in the wild-type bacteriorhodopsin and of the azide-facilitated M decay in the D96N mutant. Another pathway of the M decay is predominant at pH > 5. This pathway is insensitive to glutaraldehyde and some other similar inhibitors (lutetium ions, sucrose and glycerol). On the other hand, it is sensitive to the pK changes of the group X (Glu-204) in the outward proton pathway. Possibly, the M decay through this pathway represents a reverse H+ transport process (the proton uptake from the external surface) and proceeds via the L intermediate.
Radionov
A N
AN
Department of Photobiochemistry, A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russian Federation.
Kalaidzidis
I V
IV
Kaulen
A D
AD
D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009154:Mutation; D009994:Osmolar Concentration
D001436:Bacteriorhodopsins