The inhibition of photoreactions of chloroplasts by 2-alkyl-4-hydroxyquinoline N-oxides

Abstract

2-Heptyl-4-hydroxyquinoline N-oxide and 2-nonyl-4-hydroxyquinoline N-oxide were found to be potent inhibitors of some of the photoreactions catalysed by Swiss-chard chloroplasts. Their quantitative effects are reported on the Hill reaction, cyclic photophosphorylation in the presence of different catalysts and open photophosphorylation in the presence of ferricyanide or triphosphopyridine nucleotide. By far the most resistant reaction was the cyclic photophosphorylation dependent upon the presence of phenazine methosulphate. The most sensitive were the reduction and associated phosphorylation of ferricyanide. Inhibition of the latter by 50% was observed with 0.2 uM concentrations of the nonyl derivative. By analogy with the inhibition caused by 3-(p-chlorophenyl)-ll-dimethy-lurea, it is suggested that the quinoline N-oxides react with a site on the oxygen-evolution pathway.