Membranes of Rhodopseudomonas sphaeroides. VII. Photochemical properties of a fraction enriched in newly synthesized bacteriochlorophyll a-protein complexes.
Previous pulse-chase studies have shown that bacteriochlorophyll a-protein complexes destined eventually for the photosynthetic (chromatophore) membrane of Rhodopseudomonas sphaeroides appear first in a distinct pigmented fraction. This rapidly labeled material forms an upper band when extracts of phototrophically grown cells are subjected directly to rate-zone sedimentation. In the present investigation, flash-induced absorbance changes at 605 nm have demonstrated that the upper fraction is enriched two-fold in photochemical reaction center activity when compared to chromotophores; a similar enrichment in the reaction center-associated B-875 antenna bacteriochlorophyll complex was also observed. Although b- and c-type cytochromes were present in the upper pigmented band, no photoreduction of the b-type components could be demonstrated. The endogenous c-type cytochrome (Em = +345 mV) was photooxidized slowly upon flash illumination. The extent of the reaction was increased markedly with excess exogenous ferrocytochrome c but only slightly in chromatophores. Only a small light-induced carotenoid band shift was observed. These results indicate that the rapidly labeled fraction contains photochemically competent reaction centers associated loosely with c-type and unconnected to b-type cytochrome. It is suggested that this fraction arises from new sites of cytoplasmic membrane invagination which fragment to form leaky vesicles upon cell disruption.
D020130:Bacterial Chromatophores / Q000378:metabolism; D001426:Bacterial Proteins / Q000032:analysis*; D001429:Bacteriochlorophylls / Q000032:analysis*; D002734:Chlorophyll / Q000031:analogs & derivatives*; D003624:Darkness; D007425:Intracellular Membranes / Q000378:metabolism; D007700:Kinetics; D008027:Light; D008565:Membrane Proteins / Q000032:analysis; D010084:Oxidation-Reduction; D010788:Photosynthesis; D012242:Rhodobacter sphaeroides / Q000378:metabolism*; D013053:Spectrophotometry
D001426:Bacterial Proteins; D001429:Bacteriochlorophylls; D008565:Membrane Proteins; D002734:Chlorophyll