The effects of partial and selective reduction in the components of the proton-motive force on lactose uptake in Escherichia coli

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Abstract
The relationships between the steady state lactose accumulation (.DELTA.plac) in E. coli and the magnitude of the membrane potential (.DELTA..phi.) and pH gradient (.DELTA.pH) were studied at pH 5.5 and pH 7.5. An attempt was made to differentiate between 2 possible means by which lactose accumulation may be reduced below the proton motive force (.DELTA.p). The hypotheses tested were that .DELTA..phi. and .DELTA.pH were not equivalent in driving lactose transport and that slip reactions (.beta.-galactoside exit via the carrier without a proton) may reduce accumulation. The data supported the latter hypothesis; these conclusions are tempered by the observation that the apparent stoichiometry (.DELTA.plac/.DELTA.p) increases to a value of at least 2 at values of .DELTA.p below 130mV.