The Effect of Acidic pH on the Spectral Properties of Bacteriorhodopsin

[摘要] Purple membrane from Halobacterium halobium was incorporated into 7.5% polyacrylamide gels. Absorption and circular dichroic spectra of purple membrane incorporated with gels were obtained at various pH. The spectra of these gels measured at pH 7.0 were essentially identical with those obtained in the aqueous suspension of purple membrane. Acid titration of the gels showed the transition to a form absorbing at 605nm (bR605acid) at pH 2.6, and to a second form at 565nm (bR565acid) at pH 0.8. Dark-adapted gels showed an isosbestic point for each transition whereas light-adapted gels did not. Visible CD spectra of bR570LA, bR305acid and bR565acid all showed the typical bilobed pattern. CD spectra measured at UV wavelength region were also independent of the variation of pH in terms of molar ellipticity and spectral shape. The protonated species bR605acid may be one of the intermediates formed during the normal photochemical cycle of purple membrane. Most probably, the species bR605acid is considered to be O640 in the cycle.

[学科分类] 化学（综合）