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

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.

Acidification of the Medium Associated with Normal and Fusicoccin‐Induced Seed Germination

“…If this were also the case in the seeds, the energy provided by the gradient could be used in the transport of solutes inside the cell. Similar events have been observed in bacteria and yeasts (Pavlasova andHarold 1969, Eddy andNovacki 1971) and some preliminary results have been obtained in meristematic apices in the presence of FC (Rasi-Caldogno and Lir 1974).…”

The mechanism of action of chlorhexidine

“…The proton conduction system used here was similar to that used by other workers [7,8]. Several known uncouplers were used: tribrominated salicylanilide (TBS) and dinitrophenol (DNP) as well as CHX and polymyxin B.…”

The Effect of the Phenolic Antibacterial Agent Fentichlor on Energy Coupling in Staphylococcus aureus

“…Because there is no evidence of respiratory inhibition a t bacteriostatic concentrations it has been deduced that the action must involve energy coupling and transfer within the cell rather than that of energy release and, because these compounds caused uncoupling of oxidative phosphorylation in mitochondria1 preparations, it was postulated originally that oxidative uncoupling could also be responsible for inhibitory effects in bacterial cells. However, selective inhibition of energy-dependent metabolic activities is also found in Staphylococcus aureus and Escherichia coli under anaerobic conditions (Hamilton, 1968 ;Pavlasova & Harold, 1969) and in the fermentative organism, Streptococcus faecnlis (Harold & Baarda, 1968). The evidence indicates that in these systems, the inhibitory effects are due to specific disruption of active transport in the membrane.…”