The effect of gramicidin on ATP synthesis in pea chloroplasts: two modes of phosphorylation

The effect of gramicidin on the phosphorylation rate, electron flow and light-induced H²⁺ uptake (ΔH⁺) in chloroplasts with methyl viologen (MV) or phenazine methosulfate (PMS) added has been studied. In the presence of MV low concentrations of gramicidin (~10⁻⁹ M) were shown to inhibit the phosphorylation rate up to 80–90% of the initial value, without changing either the electron transport rate or ΔH⁺ value. Two components of phosphorylation have been identified in the presence of PMS - the first is DCMU-sensitive, which was suppressed by low gramicidin concentrations (< 10⁻⁹ M) and the second - DCMU-insensitive component, which was suppressed by high gramicidin concentrations (~10⁻⁷ M) exclusively, the high gramicidin concentration inducing the ΔH⁺ value fo fall.