Isolation and Characterisation of Oxygen Evolving Photosystem II Core Complexes from Spinach in the Presence of Glycine Betaine

Abstract

PSII contains more than 22 polypeptides (1), of which at least nine are necessary for optimal plastoquinone reduction and oxygen evolution (2). Six of these subunits are integral membrane proteins known as D1, D2, a heterodimeric Cytochrome b559 (Cyt b559), CP47 and CP43, while the three remaining extrinsic polypeptides have molecular masses of 33, 23 and 17 kDa. These three extrinsic proteins play an important role in the photosynthetic evolution of oxygen. Although the water splitting reaction can occur in their absence, the oxygen evolution process is stable and highly efficient only when they are properly attached to the PS II complex. It has been shown that glycine betaine (N-trimethyl glycine) stabilises oxygen evolution of PSII particles against thermal (3), alkaline pH (4) and salt inactivation (5). In the work presented here, isolation and characterisation of oxygen evolving PSII core complexes purified in the presence of glycine betaine (GlyB) are reported.