Abstract

Photochemical cycles of bacteriorhodopsin have been studied on the aspects of proton pumping and analogy to visual pigments [1]. The cycle of the light-adapted purple membrane (bR₅₆₈) has extensively been studied. Four intermediates, K(batho),L,M, and O, are established [2-3]. The comparison between the photocycle of bacteriorhodopsin in low pH and that in neutral pH will be helpful for understanding the mechanism of proton pumping. Oesterhelt and Stoeckenius reported that the absorption maximum of bR₅₆₈ shifts to 605 nm in low pH suspension [1]. Mowery et al. reported the dynamical behavior of acidified purple membrane (bR₆₀₅) in the time region between 80 μs to 10 ms [4]. Recently we studied the dynamical behaviors of bR₆₀₅ fin in the time region between 21 ps and 50 μs and reported that formation rates of K and L were identical with those of bR₅₆₈ and that the formation of M, Schiff base of which is unprotonated [5], was blocked in low pH suspension [6]. In the present work we discuss the effect of pH on the bacteriorhodopsin photocycle in picosecond regime.

© 1984 Optical Society of America