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J Bacteriol. 1969 April; 98(1): 198-204
Copyright © 1969 American Society for Microbiology. All Rights Reserved.

Energy Coupling in the Transport of ß-Galactosides by Escherichia Coli: Effect of Proton Conductors

^a Division of Research, National Jewish Hospital, and Department of Microbiology, University of Colorado School of Medicine, Denver, Colorado 80206

ABSTRACT

Escherichia coli accumulates thiomethyl-ß-D-galactoside against a concentration gradient under anaerobic conditions. The accumulation was abolished by carbonylcyanide m-chlorophenylhydrazone, tetrachlorosalicylanilide, 2,4 dinitrophenol, and other uncouplers of oxidative phosphorylation even though oxidative phosphorylation would not be expected to occur anaerobically. In the presence of the uncouplers, the ß-galactoside carrier remained functional and catalyzed equilibration of thiomethylgalactoside across the membrane. The uncouplers did not inhibit the generation of adenosine triphosphate or protein turnover, or the accumulation of -methylglucoside and glycerol by phosphorylation. We conclude that, at least anaerobically, uncouplers of oxidative phosphorylation do not interfere with energy metabolism in general, but prevent the utilization of metabolic energy for the active transport of galactosides. The uncouplers also facilitate passage of protons across the membrane. Various hypotheses are considered to explain why a proton-impermeable membrane may be required for active transport of galactosides and other substrates.

¹ Permanent address: Institute of Microbiology, Czechoslovak Academy of Sciences, Prague, Czechoslovakia.

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