Effect of a light-induced pH gradient on purple-to-blue and purple-to-red transitions of bacteriorhodopsin.

摘要: Bacteriorhodopsin-containing vesicles that were able to alkalize the extravesicular medium by greater than 1.5 pH units under illumination, i.e., inside-out vesicles, reconstituted reverse-phase evaporation with Halobacterium halobium polar lipids or exogenous phospholipids. Acid titration of a dark-adapted sample was accompanied color change from purple blue (pKa = 2.5-4.5 in 0.15 M K2SO4), and alkali resulted formation red species absorbing maximally at 480 nm 7 9), pKa values extents these changes being dependent on nature lipid. When vesicle suspension neutral weakly acidic irradiated continuous light so large gradient generated across membrane, either purple-to-blue purple-to-red transition took place. The light-induced significant an unbuffered correlated medium. result suggests is driven side, C-terminal membrane surface. In presence buffer molecules outside, dominant induced transition, which seemed be due decreasemore » intravesicular pH. But apparently inconsistent obtained when acidified HCl pulse, rapid blue. We arrived following explanation: two bR isomers, one containing all-trans-retinal other 13-cis-retinal, respond differently this relation, full adaptation not achieved significant.« less