Transport of Cyclitols by a Proton Symport in Klebsiella aerogenes

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Abstract
The respiration and the ATP content of K. aerogenes in the presence of various inhibitors were compared to the transport of scyllo-inositol. The ATPase was inhibited by dicyclohexyl carbodiimide. The transport was tested in anaerobiosis and aerobiosis. ATP or respiration apparently can sustain the transport activity in independent manner. The energy derived from the respiratory chain reactions or the ATP hydrolysis results in electrogenic extrusion of protons. The electrochemical potential created drives the accumulation of scyllo-inositol, as shown by an increase of pH of the medium on addition of the substrate to cells in anaerobiosis. With non-induced cells no pH change occurs, which shows that proton flow is really linked to the transport. No H+/Na+ or K+ exchange is observed and the proton conductor carbonylcyanide m-chlorophenylhydrazone abolishes the pH shift caused by substrate addition. The stoichiometry of the symport H+/cyclitol is 1 and the half-maximum value of the pH variation as a function of the amount of scyllo-inositol added corresponds to a concentration of scyllo-inositol very close to the KT of influx.