Valinomycin pulse-induced phosphorylation of ADP in dark anaerobic cells of the cyanobacteriumAnacystis nidulans

Abstract

Addition of valinomycin to dark anaerobic suspensions ofAnacystis nidulans resulted in a transient hyperpolarization of the electrical potential across the cell membrane (ΔΨCM) and seen from anilinonaphthalenesulfonate (ANS) fluorescence quenching and from distribution ratios of3H-tetraphenylphosphonium (TPP+) and14C-thiocyanate (SCN−). At the same time a similar transient increase of intracellular ATP levels was observed, which was paralleled by decreasing ADP levels and eliminated by the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP) and the F0F1-ATPase inhibitors dicyclohexylcarbodiimide (DCCD) and 7-chloro-4-nitrobenz-2-oxa-1,3-diazole (NBD), and in the presence of K+ in the medium. Since the steady-state concentration of K+ in dark anaerobic cells was around 150 mM, it is concluded that a valinomycin-induced K+ diffusion potential across the cell membrane can serve as an energy source for ATP synthesis by a reversible H+-ATPase present in the membrane.