Observations on light-induced oxidation reactions in the electron transport system of Chromatium.

Light-induced cytochrome oxidations in Chromatium subchromatophore particles were studied in detail. These reactions were found to be dependent not only on redox potential, but also on the efficiency of coupling of the redox buffer electrons to the cytochrome system. Light-induced oxidation of the high potential cytochrome (c-556) was dependent on (a) the availability of reduced cytochrome and (b) the rate of light-induced oxidation (as determined by light intensity) vs. rate of cytochrome rereduction. Chromatium high potential iron-sulfur protein ("HiPISP") enhanced the rate of c-556 rereduction by mediating electron flow from artificial redox buffers to c-556. In these experiments, the light-induced oxidation of the low potential cytochrome (c-552.5) is dependent not only on the above parameters, but also on the rate of oxidation of the primary electron acceptor X. The interactions of purified Chromatium cytochromes with the light-induced cytochrome oxidation system are discussed.