Relationship between the octanol-water partition coefficient of tertiary amines and their effect of ?selective? uncoupling of photophosphorylation

Abstract

A series of tertiary amines was investigated for effects on the transmembrane proton potential difference (Δ [Formula: see text]H), on photophosphorylation and on electron-flux control related to the intrathylakoid proton potential ([Formula: see text]HI), using isolated chloroplasts ofSpinacia oleracea L. As indicated by 9-aminoacridine fluorescence and [14C]methylamine uptake, all amines studied inhibited a build-up ofΔ [Formula: see text]H and, in parallel, ATP synthesis. Even whenΔ [Formula: see text]H was low, strong[Formula: see text]H1-dependent electron-flux control was observed under the influence of tertiary amines. The strength of flux control in the presence of lowΔ [Formula: see text]H and the effectiveness of inhibition of ATP synthesis linearly increased with the lipophilicity of the amines. The most effective of the amines tested caused 50% inhibition of ATP synthesis at a concentration of 6 μM, which is about 1000-fold lower than the concentration required for inhibition by methylamine. The data presented indicate the existence of two proton domains in the thylakoid vesicles, one of them feeding the ATP-synthase, the other the sites of pH-dependent electron-flux control. It is concluded that tertiary amines develop their action in a lipophilic domain of the thylakoid membrane, in the vicinity of the ATP-synthase complex. A mechanism for 'selective' uncoupling and for the maintenance of[Formula: see text]HI-dependent electron flux control in the presence of lowΔ [Formula: see text]H is discussed.