. "Bacillus subtilis yheL encodes a Na(+)/H(+) antiporter, whereas its paralogue, yqkI, encodes a novel antiporter that achieves a simultaneous Na(+)/H(+) and malolactate antiport. B. subtilis yufR, a control in some experiments, encodes a Na(+)/malate symporter. YqkI complemented a malate transport mutant of Escherichia coli if Na(+) and lactate were present. YheL conferred Na(+) uptake capacity on everted membrane vesicles from an antiporter-deficient E. coli mutant that was consistent with a secondary Na(+)/H(+) antiport, but YqkI-dependent Na(+) uptake depended on intravesicular malate and extravesicular lactate. YqkI-dependent lactate uptake depended on intravesicular malate and extravesicular Na(+). YqkI mediated an electroneutral exchange, which is proposed to be a malic(-2)-2H(+) (or fully protonated malate)/Na(+)-lactate(-1) antiport. Because the composite YqkI-mediated exchanges could be driven by gradients of the malate-lactate pair, this transporter could play a role in growth of B. subtilis on malate at low protonmotive force. A mutant with a disruption of yqkI exhibited an abrupt arrest in the mid-logarithmic phase of growth on malate when low concentrations of protonophore were present. Thus growth of B. subtilis to high density on a putatively nonfermentative dicarboxylic acid substrate depends on a malolactate exchange at suboptimal protonmotive force." . . . "J. Biol. Chem." . "Ito M." . "Guffanti A.A." . "Krulwich T.A." . "Wei Y." . "2000"^^ . "30287-30292" . "Bacillus subtilis YqkI is a novel malic/Na+-lactate antiporter that enhances growth on malate at low protonmotive force." . "275" . "doi:10.1074/jbc.M001112200" .