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

Summary

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.

Photodenitrifier, K⁺/H⁺ antiporter, transmembrane pH gradient, K⁺ pulse, electrogenicity