Energy transduction in Escherichia coli: physiological and biochemical effects of mutation in the uncB locus

Abstract

The transduction of energy through biological membranes was investigated in E. coli strains defective in the ATP synthetase complex. Everted vesicles prepared from strains containing an uncA or uncB mutation were compared with those of the parental strain of their ability to couple energy derived from the oxidation of substrates by the electron transport chain or from the hydrolysis of ATP by the Mg2+-adenosine triphosphatase, as measured by the energy-dependent quenching of quinacrine fluorescence or the active transport of 45Ca2+. Removal of the Mg2+-adenosine triphosphatase from membranes derived from the parental or an uncA strain caused a loss of energy-linked functions and a concomitant increase in the permeability of the membrane for protons. Proton impermeability was restored by treatment with N,N'-dicyclohexylcarbodiimide. When membranes of the uncB strain were treated in a similar manner, there was no loss of respiratory-driven functions, nor was there a change in proton permeability. These observations suggest that the uncB mutation specifically results in alteration of an intrinsic membrane protein portion of the ATP synthetase complex, leading to the loss of the proton channel necessary for the generation or utilization of the electrochemical gradient of protons by that complex. Loss of the function of the proton channel is believed to prevent the transduction of energy through the ATP synthetase complex.