Na+ and K+ transport in a photodenitrifier, Rhodopseudomonas sphaeroides f.sp. denitrificans

Abstract

Washed cells of Rhodopseudomonas sphaeroides f.sp. denitrificans depleted of cellular K+ by treatment with diethanolamine contained less than 5 mM K+. The K+-depleted cells accumulated 22Na+ only when there was no diethanolamine in the external buffer (50 mM Tris–HCl, pH 7.5). Studies with 22Na+-loaded cells indicate that this photodenitrifier had antiporters for Na+–H+, K+–Na+, and K+–H+ and lacked a respiration (denitrification) dependent Na+ pump. The K+–Na+ antiporter was electrogenic and required proton-motive force for its operation. Thus the addition of either NaCl or KCl to K+-depleted cells resulted in a depolarization of Δψ, both in light and in the dark, by 10–35 mV, which was partially compensated for by a concomitant increase (5–13 mV) in ΔpH.