title: Stable photobleaching of P840 in Chlorobium reaction center preparations: presence of the 42-kDa bacteriochlorophyll a protein and a 17-kDa polypeptide.
abstract: Simple procedures for the anaerobic preparation of photoactive and stable P840 reaction centers from Chlorobium tepidum and Chlorobium limicola in good yield are presented and quantitated. The subunit composition was tested by cosedimentation in sucrose density gradients. For C. limicola, it minimally comprises four subunits: the P840 reaction center protein PscA, the BChla antenna protein FMO, the FeS protein PscB with centers A and B, and a positively charged 17-kDa protein denoted PscD. The preparation from Chlorobium tepidum additionally contained PscC, a cytochrome c-551. The BChla absorption peak of the purified complexes was at 810 nm, with a shoulder at 835 nm. The ratio of the shoulder to the peak was 0.25, which corresponds to 1 reaction center per 70 BChla molecules if a uniform extinction coefficient of BChla is assumed. However, bleaching at 610 nm in continuous light corresponded up to 1 photoactive reaction center per 50 BChla molecules. Therefore, either the extinction coefficient of BChla in the reaction center is overestimated or the one for photobleaching is underestimated. In any case, the major portion of the reaction center was photoactive in the preparations. A P840 reaction center subcomplex, lacking PscD and deficient in FMO and PscB, but retaining the cytochrome c subunit, was obtained as a side product. It was photoinactive and had an absorption peak at 814 nm and a 835/814 absorbance ratio of 0.42. FMO and PscB show the tendency to form a complementary subcomplex. FMO and PscD are apparently required to stabilize the photoactive reaction center, while the cytochrome c subunit is not.
authors.affiliation: Lehrstuhl für Zellbiologie und Pflanzenphysiologie, Universität Regensburg, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Hager-Braun
authors.forename: D L
authors.initials: DL
authors.lastname: Xie
authors.forename: U
authors.initials: U
authors.lastname: Jarosch
authors.forename: E
authors.initials: E
authors.lastname: Herold
authors.forename: M
authors.initials: M
authors.lastname: Büttner
authors.forename: R
authors.initials: R
authors.lastname: Zimmermann
authors.forename: R
authors.initials: R
authors.lastname: Deutzmann
authors.forename: G
authors.initials: G
authors.lastname: Hauska
authors.forename: N
authors.initials: N
authors.lastname: Nelson
mesh_terms: D000465:Algorithms; D000595:Amino Acid Sequence; D000693:Anaerobiosis; D001429:Bacteriochlorophylls / Q000378:metabolism*; D001483:Base Sequence; D002462:Cell Membrane / Q000378:metabolism; D002499:Centrifugation, Density Gradient; D002848:Chromatography, DEAE-Cellulose; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010782:Photolysis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D011487:Protein Conformation; D013045:Species Specificity; D013053:Spectrophotometry; D016999:Sulfur-Reducing Bacteria / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D046911:Macromolecular Substances; D045322:Photosynthetic Reaction Center Complex Proteins