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Interaction of photosystem II proteins with non-aggregated membranes constituted of phosphatidylglycerol and the electrically neutral phosphatidylcholine enhances the oxygen-evolving activity

1998; Elsevier BV; Volume: 91; Issue: 2 Linguagem: Inglês

10.1016/s0009-3084(97)00107-2

1873-2941

Emmanuel K. Nénonéné, M. Fragata,

Photoreceptor and optogenetics research

This work investigates the role of the relative content of phosphatidylglycerol (PG) and the electrically neutral phosphatidylcholine (PC) on the oxygen evolution (OE) in the photosystem II (PSII) complex in the pH range 4.5–9.5. For this purpose, PSII particles were incorporated into non-aggregated membranes constituted of PC (PSII–PC) or PG (PSII–PG), and mixtures of PC and PG (PSII–PCPG). The major results are: (i) In solutions at pH 6.5, the PSII–PCPG membranes having a low PC content, e.g. 0.3 mol PC/mol PG, display only a slight OE augmentation in relation to the oxygen evolution observed in PSII particles in the absence of lipids. This contrasts with the OE activity observed in PSII–PCPG vesicles containing a high PC concentration, e.g. 1 or 3 mol PC/mol PG, where the oxygen evolution increases to 132 or 143% of the OE rate observed in PSII in the absence of lipids. Moreover, these OE levels are of the order of those observed previously in membranes prepared with the nonionic digalactosyldiacylglycerol (PSII–DGDG) [Fragata, M., Menikh, A., Nénonéné, E.K., 1994. Functional and structural aspects of the thylakoid lipids in oxygen evolution in photosystem II. Trends Photochem. Photobiol. 3, 201–210.]; (ii) In solutions at pH 6.5, the PSII–PCPG membranes containing a low PC content, e.g. 0.3 mol PC/mol PG, display systematically a significant decrease of oxygen evolution to levels below those observed in PSII–PG. The cooperative effect of PC and PG on the enhancement of oxygen evolution is only apparent in PSII–PCPG vesicles prepared with a high PC concentration, e.g. 1 or 3 mol PC/mol PG. In addition, the loss of oxygen-evolving activity observed in PSII particles in the absence of lipids is reversed in PSII–PCPG membranes having a high PC content. That is, the OE activity increases from 18% at pH 4.5 or 13% at pH 9.5, to about 60% at either pH 4.5 or 9.5. An important outcome in this study is that in mixed-lipid membranes constituted of phosphatidylglycerol and the electrically neutral phosphatidylcholine, the hydrophobic effect or the formation of hydrogen bonds have a more preponderant role than the electrostatic interactions in the enhancement of the oxygen evolution in the PSII complex.