A Novel Type of Coupling Between Proline and Galactoside Transport inEscherichia coli

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Abstract
Exit of thiomethylgalactoside (TMG) from preloaded cells induced the accumulation of proline. Likewise, proline exit stimulated TMG accumulation. Since a proton ionophore (carbonyl-cyanide-m-chlorophenylhydrazone) abolished these effects, a proton-motive force was implicated as the “intermediate” in the coupling reaction. The evidence suggests that the exit of TMG resulted in proton exit, which produced either a membrane potential (inside negative) or a pH gradient (outside acid) or both. This inwardly directed protonmotive force provided the energy for proline entry and accumulation. Thus the energy coupling was not via a common transport protein but by proton movements which coupled the two separate H+-dependent transport processes.