H+ and K+ efflux associated with NH4+ uptake in Anabaena cylindrica cells in the dark.

Abstract

Uptake of NH4+ by Anabaena cells in the dark at the physiological pH range of 6 to 8 occurred only under aerobic conditions and was accompanied by an efflux of H+ ions. Uptake of NH4+ also stimulated a K+ net efflux in the dark but not in the light. Uptake of NH4+ and efflux of H+ and K+ were strongly inhibited by DCCD, an inhibitor of H+-translocating ATPase. A protonophore CCCP, known to inhibit NH4+ uptake, greatly stimulated K+ efflux. It isconcluded that the uptake of NH4+ is an energy-dependent process and may be coupled to the H+ efflux. The K+ efflux may be secondarily stimulated by the NH4+ uptake.