K+-independent effects of valinomycin in photosynthetic systems

With chromatophores ofRhodospirillum rubrum, valinomycin inhibited electron transport in the presence or absence of K⁺. NH₄Cl had no effect on photophosphorylation but uncoupled with valinomycin present. ATPase activity was stimulated by NH₄Cl plus valinomycin but not by either alone. K⁺ partially reversed the inhibition of phosphorylation and the stimulation of ATPase by valinomycin plus NH₄Cl.With chloroplasts, valinomycin inhibited coupled but not basal electron transport. The inhibition was only partially reversed by uncouplers. Valinomycin stimulated the light-activated Mg²⁺-dependent ATPase similar to several uncouplers such as quinacrine, methylamine, and S-13. In addition, valinomycin inhibited delayed light emission and stimulated the H⁺/e^– ratio. These contrasting activities in chloroplasts are not easily explained.Contribution number 389 of the Charles F. Kettering Research Laboratory.