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A MICROSECOND KINETIC STUDY OF THE PHOTOGENERATED MEMBRANE POTENTIAL OF BACTERIORHODOPSIN WITH A FAST RESPONDING DYE
Author(s) -
EHRENBERG BENJAMIN,
MEIRI ZVI,
LOEW LESLIE M.
Publication year - 1984
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1984.tb03428.x
Subject(s) - bacteriorhodopsin , microsecond , chemistry , chromophore , photochemistry , proton , kinetics , schiff base , membrane potential , halobacterium salinarum , membrane , crystallography , optics , biochemistry , physics , quantum mechanics
— Bacteriorhodopsin is a light activated proton pump which generates proton and electric gradients across the cytoplasmic membrane of Halobacterium halobium. In this study, a dye whose fluorescence intensity responds rapidly to membrane potential was used to follow the evolution of the potential on liposomes reconstituted with bacteriorhodopsin, in the microseconds time domain. By comparing the formation kinetics of the potential to those of the long‐lived intermediate species in the bacteriorhodopsin photocycle, M 412 , both in H 2 O and 2 H 2 O suspensions, we can draw the following conclusion: the electric potential onset time is 20 μs after initiation of the illumination. The triggering of the potential is not the formation of the M 412 intermediate, which was hitherto considered to be the first species in the bacteriorhodopsin cycle which has an unprotonated Schiff base linkage at the retinal chromophore. Rather, the potential forms at the transition of the L 550 intermediate to the species X which precedes M 412 or even at the preceding conversion of K 590 to L 550 .