Kinetics of the electrogenic step and cytochrome b6 and f redox changes in chloroplasts

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Abstract
The spectroscopic measurements of the slow phase of the electrochromic effect and the redox kinetics of cytochrome b 6 and f provide strong evidence that a Q cycle operates in chloroplasts under conditions of non‐cyclic electron transport. The effect of HQNO and DBMIB on the extent and kinetics of these light‐induced changes places several constraints on the mechanism of quinol oxidation by the cyt. b/f—FeS complex: for each electron removed from the cyt. b/f—FeS complex by P700 an additional charge is transferred across the membrane; the cyclic pathway of electrons involved in quinol oxidation by the cyt. b/f—FeS complex includes at least one of the two b6 cytochromes; the electrogenic step associated with quinol oxidation is subsequent to the reduction of at least one cytochrome b6 quinol oxidation may proceed in a stepwise manner, with the first electron going to cytochrome b6 and the second electron going to the FeS center and cytochrome f.