Fusion of liposomes and chromatophores of Rhodopseudomonas capsulata: effect on photosynthetic energy transfer between B875 and reaction center complexes.

AUTOR(ES)

Takemoto, J Y

RESUMO

The photosynthetic chromatophore membranes of Rhodopseudomonas capsulata were fused with liposomes to investigate the effects of lipid dilution on energy transfer between the bacteriochlorophyll-protein complexes of this membrane. Phosphatidylcholine-containing liposomes were mixed with chromatophores at pH 6.0 to 6.2, and the mixture was fractionated on discontinuous sucrose gradients into four membrane fractions with lipid-to-protein ratios that varied 11-fold. Freeze-fracture electron microscopy revealed that the fractions contained closed vesicles formed by the fusion of liposomes to chromatophores. Particles with 9-nm diameters on the P fracture faces did not appear to change in size with increasing lipid content, but the number of particles per membrane area decreased proportionally with increases in the lipid-to-protein ratio. The bacteriochlorophyll-to-protein ratios, electrophoretic polypeptide profiles on sodium dodecyl sulfate-polyacrylamide gels, and light-induced absorbance changes at 595 nm caused by photosynthetic reaction centers were not altered by fusion. The relative fluorescence emission intensities due to the B875 light-harvesting complex increased significantly with increasing lipid content, but no increases in fluorescence due to the B800-B850 light-harvesting complex were observed. Electron transport rates, measured as succinate-cytochrome c reductase activities, decreased with increased lipid content. The results indicate an uncoupling of energy transfer between the B875 light-harvesting and reaction center complexes with lipid dilution of the chromatophore membrane.

Documentos Relacionados

• Nitrogenase from the photosynthetic bacterium Rhodopseudomonas capsulata: purification and molecular properties.
• Isolation and characterization of a glycerol auxotroph of Rhodopseudomonas capsulata: effect of lipid synthesis on the synthesis of photosynthetic pigments.
• Femtosecond spectroscopy of excitation energy transfer and initial charge separation in the reaction center of the photosynthetic bacterium Rhodopseudomonas viridis
• Mutational and Physiological Enhancement of Photosynthetic Energy Conversion in Rhodopseudomonas capsulata
• H2 metabolism in the photosynthetic bacterium Rhodopseudomonas capsulata: H2 production by growing cultures.