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 is
concluded 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.