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861.
The Photosystem I reaction centre contains two groups of iron-sulphur centres: Fe-SA and Fe-SB with redox potentials between ?510 and ?590 mV, and Fe-SX with redox potential about ?700 mV. Spin quantitation (Heathcote, P., Williams-Smith, D.L. and Evans, M.C.W. (1978) Biochem. J. 170, 373–378) and Mössbauer spectroscopy (Evans, E.H., Dickson, D.P.E., Johnson, C.E., Rush, J.D. and Evans, M.C.W. (1981) Eur. J. Biochem. 118, 81–84) did not show unequivocally whether Fe-SX has one or two centres. Experiments are described which support the proposal that Fe-SX has two centres. Fe-SX can be photoreduced irreversibly by 210 K illumination of dithionite-reduced samples or reversibly by 7.5 K illumination of these samples. The amplitude of the Fe-SX signal reversibly induced by illumination at 7.5 K is never more than 50% of the amplitude of the signal when Fe-SX is prereduced by room temperature illumination or by 210 K illumination. Approx. half of the Fe-SX is rapidly reduced by 210 K illumination, the remainder more slowly. The extent of reversible Fe-SX reduction and P-700 photooxidation is little affected by the fast reduction of about half of the Fe-SX. Subsequent reduction of the remaining Fe-SX is paralleled by loss of the reversible photoreaction. 相似文献
862.
A. A. Dobrovolskii A. G. Filippov A. O. Goushcha M. T. Kapoustina V. N. Karataev A. V. Privalko V. N. Kharkyanen 《Journal of biological physics》1995,21(4):265-272
The results of a study of molecular self-organization processes in the reaction centers (RC) ofRb. Sphaeroides purple bacteria by the method of pulsed optical excitation is presented. The existence of a bistability domain for the parameters of RC recovery kinetics is shown. A good agreement between the theory and experimental results is obtained. 相似文献
863.
Norma L. Pucheu Norma L. Kerber Patricia Pardo Matthias Brand Gerhart Drews A. F. García 《Archives of microbiology》1996,165(2):119-125
Membranes of Rhodobacter capsulatus strain U43 (pTX35) showed qualitatively very similar phosphorylation patterns under in vitro and in vivo conditions. In vitro,
it was irrelevant whether the phosphate source was orthophosphate or ATP. Inhibitors of electron transport did not inhibit
light-harvesting complex I (LHIα) (B870) polypeptide phosphorylation, except for o-phenanthroline, which was strongly inhibitory. Redox conditions regulated the amount of protein phosphorylated; external
redox potentials between +200 and +300 mV promoted the reaction. Phosphorylation was inhibited by uncouplers such as carbonyl
cyanide m-chlorophenyl hydrazone and nigericin plus valinomycin plus potassium ions. Inhibitors of the H+-ATPase were also inhibitory when the phosphate source was [32P]Pi or [γ-32P]ATP. From these results, it was concluded that an operative reaction center, a coupled membrane, and external redox potentials
higher than +200 mV are required for optimum LHIα phosphorylation. We also demonstrated that phosphorylation of LHIα polypeptide
occurs before insertion into the membrane and that phosphate is preferentially incorporated into specific domains within the
cytoplasmic membrane. Intracytoplasmic membranes, identified here as light membranes, were found to contain a dephosphorylated
LHIα polypeptide.
Received: 24 April 1995 / Accepted: 6 November 1995 相似文献
864.
《FEBS letters》1989,250(2):459-463
Absorption, fluorescence, and CD spectral properties of the isolated D1/D2/cytochrome b-559 photosystem II reaction center complex were examined in stabilized reaction center material at 77 K. Spectral properties were dependent on the presence or absence of 0.05% Triton X-100 in the RC suspension medium, on the redox state of pheophytin, and on the state of inactivation of the complex. The specific spectral properties of the PS II RC complex in the red suggest that the primary donor is not a bacterial-type special pair and could be a monomer. Furthermore, the spectral properties in the PS II RC may be the result of excitonic interactions among all the porphyrin molecules in the complex. Interactions between β-carotene and porphyrins indicate a significant role for β-carotene in the PS II RC. 相似文献
865.
The molecular orientation potential in an anisotropic medium was studied using the reaction field method. The interaction energy between a molecule and an anisotropic medium was calculated using the dielectric anisotropy as a perturbation parameter. We have investigated the influence of molecular geometry on the molecular orientation potential using biphenyl and terphenyl, which constitute cores of liquid crystal molecules. We have calculated the barrier height for the molecular rotation changing the twist angle between phenyl rings, using anab initio molecular orbital method. We have found that the torsional motion of the phenyl rings affects the orientation potential, and that deviation from the molecular cylindrical symmetry lowers the saddle point for the rotation. 相似文献