title: pH dependence of the formation of an M-type intermediate in the photocycle of 13-cis-bacteriorhodopsin.
abstract: An M-type intermediate is formed in the 13-cis-bR photocycle in purple membranes at high pH. This is presumably due to deprotonation of the same group whose deprotonation causes a large increase in rate of M formation in the trans-bR photocycle (the 'alkaline transition'). For Triton X-100-solubilized bR, the alkaline transition is shifted to a lower pH value by more than 2 pH units. The alkaline transition in Triton-solubilized preparations changes the efficiency of the M intermediate formation in the 13-cis-sbR photocycle. The M intermediate formation in 13-cis-sbR, as in the case of trans-sbR, is completely inhibited when the blue 'acidic' bR is formed at low pH. The protonation state of the group affecting formation of the M intermediate in 13-cis-bR at high pH and the group which is responsible for the transition to the blue acidic form influence in a similar way the equilibrium between bR isomers in the dark-adapted form as well as the rate of dark adaptation.
authors.affiliation: A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Russian Federation.
authors.forename: L A
authors.initials: LA
authors.lastname: Drachev
authors.forename: S V
authors.initials: SV
authors.lastname: Dracheva
authors.forename: A D
authors.initials: AD
authors.lastname: Kaulen
mesh_terms: D001436:Bacteriorhodopsins / Q000737:chemistry*; D003623:Dark Adaptation; D019617:Halobacterium salinarum; D006863:Hydrogen-Ion Concentration; D010777:Photochemistry
chemical_list: D001436:Bacteriorhodopsins