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A ROLE FOR MENADIONE IN THE PURPLE MEMBRANE PROTON PUMP?
Author(s) -
Renthal Robert,
Hollub Alexander
Publication year - 1988
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.1751-1097.1988.tb02810.x
Subject(s) - bacteriorhodopsin , chemistry , quantum yield , vesicle , proton , membrane , menadione , photochemistry , yield (engineering) , quinone , biophysics , biochemistry , fluorescence , biology , materials science , enzyme , physics , quantum mechanics , metallurgy
— It has been assumed that proton pumps such as purple membrane lack redox loops. However, purple membrane does contain an electron carrier. Kates et al. (Meth. Enzymol. 88,98–1 111, 1982) reported the presence of 1 mole of vitaminMK–8 to 6 mol of bacteriorhodopsin among the nonpolar lipids. Is this quinone functionally important in the proton pump mechanism? Proton pumping rates were measured with lipid‐free bacteriorhodopsin reconstituted in vesicles to which varying amounts of vitamin K 1 were added. With soybean lipids, in the presence of tetraphenyl boron, the pump quantum yield was 0.04H + /photon. This result was independent of the amount of vitamin K, added over a range of 0 to a 100‐fold mole ratio to bacteriorhodopsin. A similar result was obtained with H. halobium lipids. The pump quantum yield in vesicles is much less than reported for membrane sheets and whole cells. The results support the conclusion that a vitamin K Q‐cycle is not involved in the purple membrane proton pump.