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PHOTOCHROMIC SYNERGISM OF BACTERIORHODOPSIN‐ and HALORHODOPSIN‐MEDIATED PHOTOPHOSPHORYLATION IN Halobacterium halobium *
Author(s) -
WAGNER Gottfried,
Traulich Bernhard,
Hartmann KarlM.,
Oesterhelt Dieter
Publication year - 1987
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.1751-1097.1987.tb04786.x
Subject(s) - bacteriorhodopsin , halorhodopsin , photophosphorylation , biophysics , photochemistry , action spectrum , quantum yield , atp synthase , electrochemical gradient , halobacteriaceae , chemistry , biochemistry , biology , optics , chloroplast , physics , halobacterium salinarum , fluorescence , gene , enzyme , membrane
Quantitative action spectroscopy was performed in Halobacterium halobium. using four suited pigment mutants, namely the bacteriorhodopsin and halorhodopsin positive mutant strain M‐l (BR + , HR + ), the bacteriorhodopsin positive but halorhodopsin negative strain M‐18 (BR + , HR ‐ ), the bacteriorhodopsin negative but halorhodopsin positive strain L‐33 (BR ‐ , HR + ), and the bacteriorhodopsin and halorhodopsin negative strain L‐07 (BR ‐ , HR + ). The approached questions were: First, photoenergetic synergism of halorhodopsin and bacteriorhodopsin in intact cells; second, photochromism and cellular function of the blue light‐absorbing intermediates, i.e. M‐412 and HR‐410 in bacteriorhodopsin and in halorhodopsin, respectively. Dark‐adapted cells of mutant strain M‐l show wavelength‐dependency of quantum yield of photo‐phosphorylation, φ ATP . An 1.4‐fold enhancement was found at 575 nm wavelength where the long wavelength absorbance bands of bacteriorhodopsin and halorhodopsin intersect. The enhancement vanished after a 30 min pulse of orange light (600 Wm ‐2 bandpass from 495 to 750 nm), but was restored after a 30 min pulse of blue light (100 Wm ‐2 bandpass from 325 to 480 nm). Photoreversibility of this enhancement probably reflects phototransformation of halorhodopsin from its ground state into its inactive intermediate, HR‐410, and vice versa. The halorhodopsin‐mediated enhancement with maximum quantum yield of photophosphorylation, φ ATP = 0.06, i.e. a quantum requirement of = 17 photons/ATP, is partly substituted by a rise in phosphate potential and explained in terms of a voltage‐regulated gating effect on the H + ‐driven ATP‐synthase, superimposed on the chemiosmotic mechanism of energy coupling. The blue‐absorbing photochromic intermediate, M‐412 of bacteriorhodopsin, dissipates light energy upon photoexcitation that is reflected by a spectral decline in quantum yield of photophosphorylation to a minimum value of = 0.01 at 415 nm, i.e. a quantum requirement of = 100 photons/ATP.