Flash-induced oxidation of cytochrome b-563 in algae under anaerobic conditions: Effect of dinitrophenylether of iodonitrothymol

Abstract

Oxidation of cytochrome b-563 and reduction of oxidized plastocyanin were studied under reducing conditions in a mutant of Chlorella sorokiniana submitted to a single actinic flash. The rate of both processes is strongly decreased by addition of dinitrophenylether of iodonitrothymol. The slow increase of the membrane potential (phase b) is also strongly inhibited. Thus dinitrophenylether of iodonitrothymol is an efficient inhibitor of the site of oxidation of cytochrome b by Photosystem I (Q z site) in living algae. These results are consistent with the view that the Q z site can catalyze both cytochrome b-563 reduction and oxidation in a mechanism involving just one heme group of cytochrome b. The rate constant of the inhibitor release is higher than 100 s −1.