Regulatory Function of Cytochrome b559 in Photosystem II

Abstract

We studied the role of charge recombination reactions in Photosystem II photodamage in Synechocystis 6803 cells, in which the redox properties of Phe were modified. In the Q130E mutant where Em(Phe/Phe−) is shifted by about +35 mV photodamage and 1O2 production is decreased relative to the WT, whereas the opposite effect was observed in the Q130L mutant where Em(Phe/Phe−) is shifted by about −50 mV. We conclude that the extent of photodamage is influenced by competition of dissipation pathways of 1[P680 +Phe−] via non-radiative charge recombination and spin conversion to 3[P680 +Phe−], which regulates the yield of 3P680 and related 1O2 production. The non-radiative recombination rate of 1[P680+Phe−] is affected by Em(Phe/Phe−) whose modulation by the D1-Q130E amino acid replacement appears to be a photoprotective mechanism in cyanobacteria in vivo.