Effects of lipids on the rate-limiting steps in the dark-to-light transition of Photosystem II core complex of .

In our earlier works, we have shown that the rate-limiting steps, associated with the dark-to-light transition of Photosystem II (PSII), reflecting the photochemical activity and structural dynamics of the reaction center complex, depend largely on the lipidic environment of the protein matrix. Using chlorophyll- fluorescence transients (ChlF) elicited by single-turnover saturating flashes, it was shown that the half-waiting time (Δ ) between consecutive excitations, at which 50% of the fluorescence increment was reached, was considerably larger in isolated PSII complexes of () than in the native thylakoid membrane (TM). Further, it was shown that the addition of a TM lipid extract shortened Δ of isolated PSII, indicating that at least a fraction of the 'missing' lipid molecules, replaced by detergent molecules, caused the elongation of Δ . Here, we performed systematic experiments to obtain information on the nature of TM lipids that are capable of decreasing Δ . Our data show that while all lipid species shorten Δ , the negatively charged lipid phosphatidylglycerol appears to be the most efficient species - suggesting its prominent role in determining the structural dynamics of PSII reaction center.