Demonstration of a K⁺/H⁺exchange activity in a photodenitrifier,Rhodopseudomonas sphaeroidesforma sp.denitrificans

Washed cells of Rhodopseudomonas sphaeroides forma sp. denitrificans, grown under photodenitrifying conditions, exhibited K+ uptake dependent on the transmembrane proton gradient (Δ pH). These cells also acidified the suspension medium in response to K+ pulses both aerobically and anaerobically in light and in the dark. The results indicate that the photodenitrifier has a reversible K+/H+ exchange activity which reflects its role in regulating the intracellular K+ concentration, as well as intracellular pH. The acidification of the external medium resulting from K+ pulses was inhibited by carbonyl cyanide-m-chlorophenylhydrazone (CCCP) indicating that the antiporter is energy-dependent. Addition of KCl to washed cells depolarized the membrane potential (Δψ) with a concomitant increase in ΔpH, indicating that the K+/H+ antiporter was electrogenic.