A negatively charged region on the surface of photosystem II (PSII) near Q A has been identified as a docking site for cationic exogenous electron acceptors. Oxygen evolution activity, which is inhibited in the presence of the herbicide 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), is recovered by adding Co III complexes. Thus, a new electron-transfer pathway is created with Co III as the new terminal electron acceptor from Q A -. This binding site is saturated at ∼2.5 mM [Co III], which is consistent with the existence of low-affinity interactions with a solvent-exposed surface. This is the first example of a higher plant PSII in which the electron-transfer pathway has been redirected from the normal membrane-associated quinone electron acceptors to water-soluble electron acceptors. The proposed Co III binding site may enable efficient collection of electrons generated from photochemical water oxidation by PSII immobilized on an electrode surface.
ASJC Scopus subject areas
- Colloid and Surface Chemistry