ELECTROGENIC GLUTAMINE UPTAKE BY PEPTOSTREPTOCOCCUS-ANAEROBIUS AND GENERATION OF A TRANSMEMBRANE POTENTIAL

Peptostreptococcus anaerobius converted glutamine stoichiometrically to ammonia and pyroglutamic acid, and the Eadie-Hofstee plot of glutamine transport was biphasic. High-affinity, sodium-dependent glutamine transport (affinity constant [K-t] of 1.5 mu M) could be driven by the chemical gradient of sodium, and more than 20 mM sodium was required for half-maximal velocity. High-affinity glutamine transport was not stimulated or inhibited by a membrane potential (Delta Psi). Low-affinity glutamine transport had a rate which was directly proportional to the external glutamine concentration, required less than 100 mu M sodium, and was inhibited strongly by a Delta Psi. Cells which were treated with N,N-dicyclohexytcarbodiimide to inhibit the F1F0 ATPase still generated a Delta Psi but did so only if the external glutamine concentration was greater than 15 mM. Low-affinity glutamine uptake could not be saturated by as much as 200 mM glutamine, but glutamine(-1) accounts for only a small fraction of the total glutamine at physiological pH values (pH 6 to 7). On the basis of these results, it appeared that the low-affinity glutamine transport was an electrogenic mechanism which was converting a chemical gradient of glutamine(-1) into a Delta Psi. Other mechanisms of Delta Psi generation (electrogenic glutamine-pyroglutamate or -ammonium exchange) could not be demonstrated.