O2 reduction by photosystem I involves phylloquinone under steady-state illumination

O-2 reduction was investigated in photosystem I (PS I) complexes isolated from cyanobacteria Synechocystis sp. PCC 6803 wild type (WT) and menB mutant strain, which is unable to synthesize phylloquinone and contains plastoquinone at the quinone-binding site A(1). PS I complexes from WT and menB mutant exhibited different dependencies of O-2 reduction on light intensity, namely, the values of O-2 reduction rate in WT did not reach saturation at high intensities, in contrast to the values in menB mutant. The obtained results suggest the immediate phylloquinone involvement in the light-induced O-2 reduction by PS I. (C) 2014 Federation of European Biochemical Societies. Published by Elsevier B.V. All rights reserved.