Comparison of Ferricyanide and 2,3',6-Trichlorophenol Indophenol as Hill Reaction Oxidants.

Abstract

Using intact spinach chloroplasts, the rate of the Hill reaction with ferricyanide as a Hill oxidant is only 20-30% of the rate obtained with indophenol dye as oxidant. Dilution of the chloroplasts in NaCl solution of pH 6 was found to increase the rate of ferricyanide reduction to a level equal to that of dye reduction. This treatment decreases or abolishes the ability of the chloroplasts to catalyze photophosphorylation, increases the susceptibility of the Hill reaction to inhibition by metal chelating agents, and has no effect on the chloroplasts'' ability to photoreduce pyridine nucleotides. Light saturation curves indicate that the limitation on the Hill reaction of untreated chloroplasts with ferricyanide as oxidant is due to a limitation at some dark step. It is suggested that this limitation is due to a coupling of the electron transport system of the Hill reaction to photophosphorylation.