Does functional photosystem II complex have an oxygen channel?

Photosystem II complex (PSII) of thylakoid membranes uses light energy to o xidise extremely stable water and produce oxygen (2H(2)O --> O-2+4H(+)+4e(- )). PSII is compared with cytochrome c oxidase that catalyses the opposite reaction coupled to proton translocation. Cytochrome c oxidase has proton a nd mater channels, and a tentative oxygen channel. I propose that functiona l PSII complexes also need a specific oxygen channel to direct O-2 from the mater molecules bound to specific Mn atoms of the Mn cluster within PSII o ut to the membrane surface. The function of this channel will be to prevent oxygen being accessible to the radical pair P680(+)Pheo(-), thereby preven ting singlet oxygen generation from the triplet P680 state in functional PS II. The important role of singlet oxygen in structurally perturbed non-func tional photosystem II is also discussed. (C) 2001 Federation of European Bi ochemical Societies. Published by Elsevier Science B.V. All rights reserved .