Action Spectra for Inhibition by Light of Accumulation of Bacteriochlorophyll and Carotenoid during Aerobic Growth of Photosynthetic Bacteria

Action spectra for the inhibition by light of the accumulationof photosynthetic pigments during the aerobic growth of a photosyntheticbacterium, Rhodobacter sphaeroides, and an aerobic photosyntheticbacterium, Erythrobacter sp. strain OCh 114, were determinedover the range of wavelengths from 380 to 870 nm. The actionspectra for the inhibition of accumulation of bacteriochlorophyllin both R. sphaeroides and Erythrobacter sp. strain OCh 114indicated that the maximum inhibition occurred at approximately400 nm and a low level of inhibition occurred at 575 and 770nm. In R. sphaeroides, the action spectrum for the inhibitionof accumulation of carotenoid paralleled that for the inhibitionof accumulation of bacteriochlorophyll over the same range ofwavelengths. These results indicate that in both species, grownunder aerobic conditions, the same photoreceptor is involvedin the inhibition. One possible candidate for the relevant photoreceptormay be the precursor(s) to bacteriochlorophyll. It is possiblethat the photoreceptor is decomposed by light absorbed by itselfor by an unidentified photoreceptor that absorbs blue light(a photo-sensitizer). It is suggested that the accumulationof carotenoid is dependent on the stability of the bacteriochlorophyll. (Received September 16, 1988; Accepted March 2, 1989)     

Enzymatic properties of ubiquinol:cytochrome c2 oxidoreductase in situ in Rhodopseudomonas palustris membranes

The presence of ubiquinol:cytochrome c2 oxidoreductase was shown in the membranes from a photosynthetic bacterium, Rhodopseudomonas palustris. Some properties of the enzyme in situ were investigated. The optimal pH of this enzyme activity was 7.0 in the intact membranes. The activity was inhibited by both antimycin and myxothiazol. Maximal activity (Vmax) was 3-4 mol cytochrome c (c2) reduced/mol cytochrome c1.s. Apparent activity of the enzyme with horse heart cytochrome c as the electron acceptor decreased as the concentration of salts in the reaction mixture increased, whereas when R. palustris cytochrome c2 was used as the electron acceptor, the activity increased as the concentration of salts increased. Moreover, the activity of the enzyme did not depend on the species or concentration of anions but on both the concentration and valency of the cations of the salts. These salt effects were thought to be due to the change of effective concentration of cytochrome molecules caused by cations near the membrane surface, which was net negatively charged. Apparent Km for ubiquinol-1 was about 80 microM irrespective of the species of cytochrome and the presence of salts.     

Trimethylamine N-oxide respiration by aerobic photosynthetic bacterium, Erythrobacter sp. OCh 114

Erythrobacter sp. OCh 114, an aerobic photosynthetic bacterium, had trimethylamine N-oxide (TMAO) reductase activity, which increased when the culture medium contained TMAO. The reductase was located in the periplasm. The bacteria grew anaerobically in the presence of TMAO. These results suggested that Erythrobacter OCh 114 has the ability to reduce TMAO through the respiratory chain. The TMAO respiration system of this organism was different from those of facultative purple photosynthetic bacteria in two respects: (a) TMAO reductase did not have activity to reduce dimethyl sulfoxide and (b) soluble c-type cytochrome, cytochrome c551, and cytochrome b-c1 complex appeared to be involved. The photochemical activity, which is usually inoperative in the anaerobic cell suspension, was restored by TMAO, suggesting that the photosynthesis and the TMAO respiration share a common electron transfer chain.     

Purification and Some Properties of Soluble Cytochromes, Cytochrome c-551 and Cytochrome c-550, from a Facultative Methylotroph, Protaminobacter ruber strain NR-1

Two soluble cytochromes of the C-type, cytochrome c-551 andcytochrome c-550, were purified from the bacteriochlorophyll-containingcells of a facultative methylotroph, Protaminobacter ruber StrainNR-1, by ion-exchange chromatography and gel-filtration. Cytochrome c-551 had absorption maxima at 551, 522 and 416 nmin the reduced form, and at 525, 410 and 273 nm in the oxidizedform. This cytochrome was a slightly basic protein with an isoelectricpoint of 8.4. It had a mid-point redox potential of 272 mV atpH 7.0. The molecular weight of this protein was 13,500 and13,700 by sodium dodecylsulfate polyacrylamide gel electrophoresis(SDS-PAGE) and gel-filtration, respectively. Cytochrome c-550 had absorption maxima at 550, 522 and 415 nmin the reduced form, and at 527, 409 and 278 nm in the oxidizedform. This cytochrome was acidic, having an isoelectric pointof 4.3. It had a mid-point redox potential of 227 mV at pH 7.0.Its molecular weight was 19,500 and 22,000 by SDS-PAGE and gel-filtration,respectively. (Received August 4, 1984; Accepted October 22, 1984)     

Isolation and Purification of Cytochrome b561 from a Photosynthetic Bacterium, Rhodopseudomonas sphaeroides

Cytochrome b₅₆₁ was removed from chromatophores of a photoanaerobicallygrown Rhodopseudomonas sphaeroides by deoxycholate-cholate andTriton X-100 treatments of the chromatophores. The cytochromewas purified by ammonium sulfate fractionation and gel filtration.Its molecular weight was 45,000 (45 kD) and it was composedof three subunits with molecular weights of 23 kD, 19 kD andless than 6 kD. The cytochrome preparation had absorption maximaat 414 nm in the oxidized form, and at 428, 530 and 561 nm inthe reduced form. Its pi was 4.8. The midpoint potential ofthis cytochrome was 153 mV at pH 7.0. The compound was autooxidizable,and it had cytochrome c oxidase activity. (Received May 16, 1983; Accepted September 8, 1983)     

Binding of nonamer peptides to three HLA-B51 molecules which differ by a single amino acid substitution in the A-pocket

The interaction between 9-mer peptides and HLA-B51 molecules was investigated by quantitative peptide binding assay using RMA-S cell expressing human β2-microglobulin and HLA-B51 molecules. Of 147 chemically synthesized 9-mer peptides possessing two anchor residues corresponding to the motif of HLA-B^*5101 binding self-peptides, 27 paptides bound to HLA-B^*5101 molecules. Pro and Ala at position 2 as well as Ile at position 9 were confirmed to be main anchor residues, while Gly at position 2 as well as Val, Leu, and Met at position 9 were weak anchor residues for HLA-B^*5101. The A-pocket is suspected to have a critical role in peptide binding to MHC class I molecules because this pocket corresponds to the N-terminus of peptides and has a strong hydrogen bond formed by conserved Tyr residues. Further analysis of peptide binding to HLA-B^*5102 and B^*5103 molecules showed that a single amino acid substitution of Tyor for His at residue 171(B^*5102) and that of Gly for Trp at residue 167 (B^*5103) has a minimum effect in HLA-B51-peptide binding. Since previous studies showed that some HLA-B51 alloreactive CTL clones failed to kill the cells expressing HLA-B^*5102 or HLA-B^*5103, these results imply that the structural change of the A-pocket among HLA-B51 subtypes causes a critical conformational change of the epitope for TCR recognition rather than influences the interaction between peptides and MHC class I molecules.     

Some properties and occurrence of cytochrome c-552 in the aerobic photosynthetic bacterium Roseobacter denitrificans

Characteristics and occurrence of cytochrome c-552 from an aerobic photosynthetic bacterium, Roseobacter denitrificans, were described.Relative molecular mass of the cytrochrome was 13.5 kDa on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and 15,000 by gel filtration. This cytochrome was a acidic protein having a pI of 5.6 and E_m was +215 mV at pH 7.0. Absorption peaks were at 278, 408 and 524 nm in the oxidized form and 416, 523 and 552 nm in the reduced form.Amino acid composition and N-terminal amino acid sequence of cytochrome c-552 determined for 24 residues had low similarities to those of cytochrome c-551 of this bacterium, which is homologous to cytochrome c ₂, although the physico-chemical properties of these two cytochromes were similar to each other.Cytochrome c-552 was maximally synthesized in the light under aerobic conditions but not in the dark. The synthesis also occurred in the presence of alternative acceptors such as trimethylamine N-oxide (TMAO) and nitrate under anaerobic conditions. Our results suggest that cytochrome c-552 is involved in TMAO respiration and denitrification in R. denitrificans, although the effect of light remains to be solved.Abbreviations E_m Midpoint redox potential - PAGE Polyacrylamide ge electrophoresis - SDS-PAGE Sodium dodecyl sulfate polyacrylamide gel electrophoresis - TMAO Trimethylamine N-oxide