No abstract

Escherichia coli accumulates thiomethyl-/3-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,3-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 ca-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.

Glycolyzing cells of Streptococcus faecalis accumulate K+ with concurrent extrusion of equivalent amounts of H+ and Na+. An attempt was made to clarify the retionship between the movements of Na+ and K+. Sodium was displaced from cells glycolyzing in the presence of ammonia, diethylamine, tris(hydroxymethyl)aminomethane, and other nitrogenous cations; by contrast, K+ was completely retained. Accumulation of K+ by heterologous exchange for Na+ was not inhibited by antibiotics which facilitate diffusion of K+ across the membrane, but was blocked by proton conductors. The results indicate that extrusion of Na+ and H+ from the cells is a primary, energy-linked process which generates an electrical potential (interior negative); K+ accumulation occurs in response to this potential. Two mutants deficient in K+ accumulation and retention were examined in terms of this model. One mutant is apparently defective in exchange of K+ for H+. In the other mutant, exchange of K+ for Na+ is impaired.