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

Peptostreptococcus anaerobius converted glutamine stoichiometrically t o ammonia and pyroglutamic acid, and the Eadie-Hofstee plot of glutami ne transport was biphasic. High-affinity, sodium-dependent glutamine t ransport (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 f or half-maximal velocity. High-affinity glutamine transport was not st imulated or inhibited by a membrane potential (Delta Psi). Low-affinit y glutamine transport had a rate which was directly proportional to th e 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 gen erated a Delta Psi but did so only if the external glutamine concentra tion was greater than 15 mM. Low-affinity glutamine uptake could not b e 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 th e 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-pyro glutamate or -ammonium exchange) could not be demonstrated.