AN ARGININE ORNITHINE EXCHANGE SYSTEM IN SPIROPLASMA-MELLIFERUM

Spiroplasma melliferum cells utilize arginine via the arginine dihydro lase pathway. L-Arginine uptake by intact cells was a saturable proces s both as a function of time and arginine concentration (K-m = 40 mu M ). Uptake was not affected by ph in the range ph 5.0-8.0, or by L-citr ulline, D-arginine, L-histidine or L-canavanine at concentrations tenf old higher than that of L-arginine. In contrast, L-arginine uptake was markedly inhibited by L-ornithine and partially inhibited by L-lysine . Uptake was neither affected by protonophores nor by cation ionophore s, but was inhibited by protease treatment or by the sulfhydryl reagen ts p-chloromercuribenzoate or N-ethylmaleimide. Sealed membrane vesicl es prepared by fusing isolated S. melliferum membranes with asolectin- cholesterol vesicles catalysed a rapid exchange (t(1/2) = 1 min) betwe en arginine and ornithine. Exchange did not require ATP and could be d emonstrated in both directions, i.e. with either arginine or ornithine trapped within vesicles. These observations suggest that the driving forces for arginine uptake by whole cells are the concentration gradie nts of arginine and ornithine formed by arginine metabolism.