Abstract
Studies of the beta-galactoside transporter in inverted membrane vesicles of Escherichia coli. II. Symmetrical binding of a dansylgalactoside induced by an electrochemical proton gradient and by lactose efflux.
Highlights
The binding of 6’-(N-dansyl)aminohexyl-u-thiogalactoside (DG,) to inverted vesicles of Escherichia coli was measured by fluorescence enhancement
In addition we have shown potenthat a pH gradient across the membrane, basic inside, caused DG,; binding to inverted vesicles indicating that the entire electrochemical proton gradient is responsible for the effect
The binding of I)G,j induced by lactose efflux or the membrane potential was inhibited by the addition of ATP, showing that the vesicles which bound IIG,; were inside-out
Summary
Analogous studies of lactose transport in inverted vesicles showed that the efflux of internal [“Cllactose increased the V,;,, for uptake of [‘Cllactose but did not change the half-saturation constant. Rudnick et al [6] have reported binding of radioactive p-nitrophenyl-a-n-galactoside by right side-out vesicles This substrate was similar to dansylgalactosides in that it was bound but was not transported, and binding was increased greatly by n-lactate oxidation. They reported specific binding in the absence of energy which exhibited the same K,, but only about 10% of the maximal number of sites.
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