Localized Proton Domains in pH-Dependent Control of Photosynthetic Electron Transport under the Influence of Lipophilic Tertiary Amines
Photosynthetic electron transport is under control of the intrathylakoid proton potential,µ͂HI (1,2). When µ͂HI increases in the light, with the build-up of a transthylakoid proton gradient (Δ µ͂H), electron flow is decelerated. Two major sites of µHI-dependent feed-back control have been discussed: the reduction of the primary photosystem (PS) II acceptor QA (2) and the oxidation of plastohydroquinone at the cytochrome b/f complex (1). Under condition of photophosphorylation/µ͂H decreases and flow control is partly released. Recently, lipophilic tertiary amines were shown to be effective inhibitors of ATP synthesis and of the build-up of Δ µ͂H (3–5). The inhibition of a Δ µ͂H rise, as indicated by 9-aminoacridine (9-AA) fluorescence quenching (6) or (l4C)-methylamine uptake (7), appeared to be determinant for the decline of photophosphorylation. In this, the effects of lipophilic amines resemble ‘classical’ uncoupler effects. Nevertheless, the pH-dependent flow control was preserved in the presence of tertiary amines despite of the low Δ µ͂H observed. Control mechanisms were active although µ͂HI appeared to be low. This is in apparent contradiction to the theory of pH-dependent flow control.
KeywordsElectron Flow Tertiary Amine Photosynthetic Electron Transport Uncoupler Effect Proton Uptake
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