Light-driven reduction of oxygen as a method for studying electron transport in the green photosynthetic bacterium Chlorobium limicola

Abstract

The use of O2 uptake as a valid assay for non-cyclic photosynthetic electron flow in membranes from Chlorobium limicola is discussed. It is recommended that methyl viologen, catalase and superoxide dismutase should be added to the experimental medium. The addition of methyl viologen more than doubled the rate of O2 uptake observed on illumination with 1 mM sulphide as donor. Superoxide dismutation was shown to be efficient under the experimental conditions by means of standard additions of potassium superoxide dissolved in dimethylsulphoxide. The highest rates of light stimulated O2 uptake were obtained with sulphide as electron donor, and approached 50 μmol O2 · h-1 · mg bacteriochlorophyll c -1 with 0.2 mM sulphide. The presence of 5 mM 2-mercaptoethanol or 3 mM sulphite as electron donor led to lower light stimulated rates of O2 uptake, while 5 mM thiosulphate had little effect. The rates were insensitive to uncoupler. The light stimulated O2 uptake with 0.2 mM sulphide as donor was 20–30% inhibited by 10 μM antimycin A and 50 μM cyanide.