Light dependence of the decay of the proton gradient in broken chloroplasts

Abstract

The initial rates and steady-state values of proton uptake by broken chloroplasts have been measured as functions of light intensity at various concentrations of chlorophyll, pyocyanine, supporting electrolyte, buffer, as well as pH and temperature. Kinetic analysis of the data shows that the rate of decay of proton gradient due to backward leakage depends on light intensity. Under steady illumination, the decay constant k L is equal to k D + mR 0, where R 0 is the initial rate of proton uptake which is a function of light intensity, k D is the decay constant in the dark and m is a parameter which is independent of light intensity. Treatment of chloroplasts with lysolecithin, neutral detergent, 2,4-dinitrophenol, or valinomycin in the presence of K + increases k D without affecting m. Treatment with N, N′-dicyclohexylcarbodiimide or adenylyl imidodiphosphate under appropriate conditions decreases m without affecting k D. Treatment with glutaraldehyde makes k L independent of light intensity and hence m = 0. These results suggest that the light-dependent part (mR 0) of k L is due to leakage of protons through the coupling factor (CF 1-CF 0) complex which can open or close depending on light intensity and that the light-independent part ( k D) of the decay constant k L is due to proton leakage elsewhere.