The PSII calcium site revisited

Biological and Soft Matter Physic

Photo-CIDNP solid-state NMR on photosystems I and II: What makes P680 special?

Theoretical Physic

Flash-induced redox changes in oxygen-evolving spinach Photosystem II core particles

Flash-induced redox reactions in spinach PS II core particles were investigated with absorbance difference spectroscopy in the UV-region and EPR spectroscopy. In the absence of artificial electron accepters, electron transport was limited to a single turnover. Addition of the electron accepters DCBQ and ferricyanide restored the characteristic period-four oscillation in the UV absorbance associated with the S-state cycle, but not the period-two oscillation indicative of the alternating appearance and disappearance of a semiquinone at the Q(B)-site. In contrast to PS II membranes, all active centers were in state S-1 after dark adaptation. The absorbance increase associated with the S-state transitions on the first two flashes, attributed to the Z(+)S(1) --> ZS(2) and Z(+)S(2) --> ZS(3) transitions, respectively, had half-times of 95 and 380 mu s, similar to those reported for PS II membrane fragments. The decrease due to the Z(+)S(3) --> ZS(0) transition on the third flash had a half-time of 4.5 ms, as in salt-washed PS II membrane fragments. On the fourth flash a small, unresolved, increase of less than 3 mu s was observed, which might be due to the Z(+)S(0) --> ZS(1) transition. The deactivation of the higher S-states was unusually fast and occurred within a few seconds and so was the oxidation of S-0 to S-1 in the dark, which had a half-time of 2-3 min. The same lifetime was found for tyrosine D+, which appeared to be formed within milliseconds after the first flash in about 10% inactive centers and after the third and later flashes by active centers in Z(+)S(3).Biological and Soft Matter Physic

Circular dichroism of the peripheral chlorophylls in photosystem II reaction centers revealed by electrochemical oxidation

Visible absorption spectra and circular dichroism (CD) of the red absorption band of isolated photosystem II reaction centers were measured at room temperature during progressive bleaching by electrochemical oxidation, in comparison with aerobic photochemical destruction, and with anaerobic photooxidation in the presence of the artificial electron acceptor silicomolybdate. Initially, selective bleaching of peripheral chlorophylls absorbing at 672 nm was obtained by electrochemical oxidation at +0.9 V, whereas little selectivity was observed at higher potentials. Illumination in the presence of silicomolybdate did not cause a bleaching but a spectral broadening of the 672-nm band was observed, apparently in response to the oxidation of carotene. The 672-nm absorption band is shown to exhibit a positive CD, which accounts for the 674-nm shoulder in CD spectra at low temperature. The origin of this CD is discussed in view of the observation that all CD disappears with the 680-nm absorption band during aerobic photodestruction

Exploring the Calcium-binding site in photosystem II membranes by solid state 113 Cd-NMR

Biological and Soft Matter Physic

Heteronuclear 2D (1H-13C) MAS NMR resolves the electronic structure of coordinated histidines in light-harvesting complex II: assessment of charge transfer and electronic delocatlization effect

Solid state NMR/Biophysical Organic Chemistr

Photochemically induced dynamic nuclear polarization in the reaction center of the green sulphur bacterium Chlorobium tepidum observed by 13C MAS NMR

AbstractPhotochemically induced dynamic nuclear polarization has been observed in reaction centres of the green sulphur bacterium Chlorobium tepidum by 13C magic-angle spinning solid-state NMR under continuous illumination with white light. An almost complete set of chemical shifts of the aromatic ring carbons of a BChl a molecule has been obtained. All light-induced 13C NMR signals appear to be emissive, which is similar to the pattern observed in the reaction centers of plant photosystem I and purple bacterial reaction centres of Rhodobacter sphaeroides wild type. The donor in RCs of green sulfur bacteria clearly differs from the substantially asymmetric special pair of purple bacteria and appears to be similar to the more symmetric donor of photosystem I