Kinetics of phyllosemiquinone oxidation in the Photosystem I reaction centre of Acaryochloris marina

Light-induced electron transfer reactions in the chlorophyll a/d-binding Photosystem I reaction centre of Acaryochloris marina were investigated in whole cells by pump-probe optical spectroscopy with a temporal resolution of ~5ns at room temperature. It is shown that phyllosemiquinone, the secondary electron transfer acceptor anion, is oxidised with bi-phasic kinetics characterised by lifetimes of 88±6ns and 345±10ns. These lifetimes, particularly the former, are significantly slower than those reported for chlorophyll a-binding Photosystem I, which typically range in the 5–30ns and 200–300ns intervals. The possible mechanism of electron transfer reactions in the chlorophyll a/d-binding Photosystem I and the slower oxidation kinetics of the secondary acceptors are discussed. ► The oxidation kinetics of secondary intermediates in PS I of A. marina are biphasic. ► The decay is characterised by lifetimes of 88±6ns and 345±10ns. ► Both these lifetimes are slower than in typical Chl a-binding PS I reaction centres. ► Possible mechanism of electron transfer is discussed.