Effect of hydrocarbon chain length on the uncoupling of photophosphorylation by amines

Abstract

The effectiveness of normal aliphatic amines in uncoupling photophosphorylation in chloroplasts increases dramatically with increasing number of carbon atoms. A similar effect was observed in subchloroplast particles, except that phosphorylation in these preparations was less sensitive to inhibition by aliphatic amines with less than five carbon atoms than phosphorylation in chloroplasts. A linear relationship between the log of the concentration of the amines required to give 50% inhibition of photophosphorylation and the log of their octanol/water partition coefficients was obtained for ethyl- through hexyl-amines. A similar relationship was found for hexylthrough nonyl-amines except that the inhibition increased more dramatically with increasing chain length than for the shorter chain amines. In contrast, the log of the activity of the amines in the inhibition of hydrogen ion uptake in chloroplasts was linearily related to the log of their octanol/water partition coefficients for all amines tested. The trypsin-activated, Ca 2+-dependent adenosine triphosphatase of purified coupling factor 1 from chloroplasts was insensitive to inhibition by short chain amines, but was strongly inhibited by long chain amines. The dependency of the inhibition of this reaction by amines on their hydrocarbon chain length was similar to that observed in the inhibition of phosphorylation. The inhibition of photophosphorylation by long chain amines may, therefore, be caused in part by their effects on coupling factor 1. Phosphorylation in subchloroplast particles supplemented with valinomycin is inhibited by ammonium chloride. In the presence of these reagents, phosphorylation in subchloroplast particles may be stimulated by amines. The effectiveness of amines in stimulating phosphorylation under these conditions paralleled their effectiveness as uncouplers. This observation provides evidence that this stimulatory action of the amines is related to their action as uncouplers.