COMPLICATED CHARACTER OF THE M-DECAY PH-DEPENDENCE IN THE D96N MUTANTIS DUE TO THE 2 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 complicat ed behavior which is found to be due to the coexistence of two pathway s of the M conversion, The M decay which dominates at pH < 5 is couple d to the proton uptake from the cytoplasmic surface and proceeds proba bly through the IV intermediate, This pathway is inhibited by glutaral dehyde, the potent inhibitor of M decay in the wildtype bacteriorhodop sin and of the azide-facilitated M decay in the D96N mutant, Another p athway of the M decay is predominant at pH > 5, This pathway is insens itive to glutaraldehyde and some other similar inhibitors (lutetium io ns, sucrose and glycerol), On the other hand, it is sensitive to the p K changes of the group X (Glu-204) in the outward proton pathway, Poss ibly, the M decay through this pathway represents a reverse H+ transpo rt process (the proton uptake from the external surface) and proceeds via the L intermediate.