Abstract
The effect of several different quinolines and related compounds was investigated on electron transport and proton translocation associated with photophosphorylation in spinach chloroplasts. It was found that many quinolines, regardless of their chelating ability, strongly inhibited dimethylbenzoquinone reduction by photosystem II (PS II) or the ascorbate + diaminodurene (DAD) → methylviologen (MV) pathway in photosystem I (PS I). Ascorbate + N, N, N 1, N 1-tetramethyl- p-phenylene diamine (TMPD) oxidation by PS I could also be inhibited by some quinolines and related compounds. Three modes of action presumably explain the effects observed: (1) chelation of non-heme irons found in PS II between the plastoquinone pool and cytochrome f, (2) non-specific lipid effect on chloroplast membranes by quinoline-like nitrogen bases and (3) sulfhydryl effects on chloroplast proteins by mercaptoquinoline type substances. The inhibition of proton gradients associated with cyclic and non-cyclic photophosphorylation resulted from removal of protons by the quinolines.
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