Similarity between electron donor side reactions in the solubilized Photosystem II–LHC II supercomplex and Photosystem-II-containing membranes

The PS II–LHC II supercomplex is a novel type of oxygen evolving Photosystem II (PS II) core particle that contains the light harvesting complex proteins Lhcb1/2/4/5 in addition to the PS II reaction centre, oxygen evolving complex (OEC) and inner antennae [Hankamer et al. (1997) Eur J Biochem 243: 422–429]. The 33 and 23 kDa extrinsic proteins in these particles have been localised by image analysis of electron micrographs and averaging techniques [Boekema et al. (1998) Eur J Biochem 252: 268–276]. To assay the functionality of the water splitting complex, we compared the single flash P680+ reduction kinetics in these supercomplexes with those of PS II-rich granal stack membranes (BBYs). We found that the P680+ reduction kinetics in PS II–LHC II supercomplexes were indistinguishable from those in BBYs. We also examined a number of PS II core particles lacking the Lhcb components. All of these had different P680+ reduction kinetics, which we attributed to partial loss of OEC function before and during the measurements.