Bicarbonate-controlled reduction of oxygen by the Q_A semiquinone in Photosystem II in membranes.

ABSTRACT: Photosystem II (PSII), the water/plastoquinone photo-oxidoreductase, plays a key energy input role in the biosphere. [Formula: see text], the reduced semiquinone form of the nonexchangeable quinone, is often considered capable of a side reaction with O₂, forming superoxide, but this reaction has not yet been demonstrated experimentally. Here, using chlorophyll fluorescence in plant PSII membranes, we show that O₂ does oxidize [Formula: see text] at physiological O₂ concentrations with a t_1/2 of 10 s. Superoxide is formed stoichiometrically, and the reaction kinetics are controlled by the accessibility of O₂ to a binding site near [Formula: see text], with an apparent dissociation constant of 70 ± 20 µM. Unexpectedly, [Formula: s

SUBMITTER: Fantuzzi A 

PROVIDER: S-EPMC8833163 | biostudies-literature | 2022 Feb

REPOSITORIES: biostudies-literature