Effect of iodination of the purple membrane on the photocycle of bacteriorhodopsin

Comparison of the O640 photo‐intermediate and acid‐induced species in membrane patches from Halobacterium halobium S9 and R1mW strains

“…If the effects of low pH are due to the stabilization of the 13-cis conformation of retinal, it would be predicted that reconstituted white membrane patches should show a faster rate of light-to-dark adaptation. The rate of dark adaptation is considerably enhanced in reconstituted white membranes to a t,~ of 2 min ( fig.5) as compared to 60 min for native purple membranes [7]. The light-minus-dark difference spectrum of reconstituted white membranes shows a minimum at 505 nm, a maximum at 588 nm and an isosbestic point at 541 nm (not shown).…”

Light‐dependent trans to cis isomerization of the retinal in halorhodopsin

“…It has been suggested that this transport occurs via the reversible deprotonation of a chain of residues arranged across the membrane barrier [19,20]. Tyrosine (and perhaps tryptophan) may be elements of this chain, and indeed it has been shown that chemical modification of tyrosines [21], and particularly tyrx 1221 and tyra [23] has specific effects on the pi8ment. The photocycle of halorhodopsin is not fully described, but it is known [24-271 that the principal intermediate observed in the presence of halides absorbs near 500 nm (Pszo), while in the absence of chloride it absorbs near 640 nm (PESO).…”

Effect of salt on the tyrosine and protonated Schiff base deprotonation kinetics in bacteriorhodopsin

“…M4,, is unique, as it is the only intermediate whose Schiff base is unprotonated, while the parent pigment and all the other intermediates are protonated (4,(13)(14)(15)(16)(17). Some studies have inferred that the Schiff base deprotonation is closely associated with the proton pump mechanism (18,19) and the effect of chemically modified tyrosines on the rate of decay of MqI2 suggests a coupling between some tyrosines and M4,, (20)(21)(22)(23)(24).…”