Light-dark adaptation of bacteriorhodopsin in triton-treated purple membrane.
Solubilization of purple membrane with Triton X-100 yields Triton micelles containing bacteriorhodopsin monomers. The absorption maximum of dark-adapted solubilized bacteriorhodopsin is blue-shifted to 549 nm. Light adaption increases the absorbance by 4% and shifts the absorption maximum to 553 nm, i.e., the extent of light adaptation is considerably less than in intact purple membrane. Extraction of dark-adapted bacteriorhodopsin in Triton yields a 13-cis- to all-trans-retinal ratio of 58 : 42 which changes after light adaptation to 38 : 62. It has been shown by Sperling et al. (Sperling, W., Carl, P., Rafferty, Ch.N. and Dencher, N.A. (1977) Biophys. Struct. Mech. 3, 79-94) that light adaptation in intact purple membrane occurs through a branching of the 13-cis photoreaction cycle, so that part of the pigment during each cycle crosses over into the all-trans photoreaction cycle. We explain the decreased extent of light adaptation in solubilized bacteriorhodopsin by assuming a significant back reaction from the all-trans to the 13-cis cycle. This assumption predicts a wavelength dependence of the extent of light adaptation, which is born out by experiment.
D001436:Bacteriorhodopsins / Q000032:analysis*; D002338:Carotenoids / Q000032:analysis*; D003624:Darkness; D006217:Halobacterium / Q000032:analysis; D008027:Light; D017830:Octoxynol; D011092:Polyethylene Glycols; D013057:Spectrum Analysis; D013237:Stereoisomerism
D002338:Carotenoids; D011092:Polyethylene Glycols; D001436:Bacteriorhodopsins; D017830:Octoxynol