Stimulation and inhibition of membrane-dependent ATP synthesis in chloroplasts by artificially induced K+ gradients.

Abstract

The imposition of a potassium ion gradient simultaneous with a pH transition of Valinomycin treated spinach chloroplasts results in a modulation of ATP synthesis elicited by the acid-base transition. A gradient from the outside to the interior of the granum results in a stimulation of ATP synthesis. Under these conditions the synthesis of ATP is sensitive to the addition of dinitrophenol. A gradient of the opposite sense results in an inhibition of ATP synthesis and the yield is not further reduced by the addition of dinitrophenol. The data support the concept that ion imbalance caused by Valinomycin facilitated K+ movement across the energy conserving membrane of the chloroplast can lead to membrane potential differences of sufficient magnitude to influence the yield of ATP in a membrane-dependent energy conserving system.