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)     

Increased frequency of 6-thioguanine-resistant peripheral blood lymphocytes in Werner syndrome patients

Summary The frequency of spontaneous 6-thioguanine (TG)-resistant peripheral blood lymphocytes in five unrelated Werner syndrome (WS) patients was determined using an autoradiographic labeling assay. The average frequency of TG-resistant lymphocytes was eightfold higher in WS patients than in sex- and age-matched normal control donors. This finding and previous identification of increased spontaneous chromosomal rearrangements and deletions in WS cells or cell lines suggest that WS is a human genomic instability or mutator syndrome.     

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)     

Overexpressions of cDNAs for β-Amyloid Precursor Proteins 695, 751, and 770 Enhance the Secretion of β-Amyloid Precursor Protein Derivatives and the Survival of P19-Derived Neurons

Abstract: P19 is a C3H mouse-derived line of multipotent embryonic carcinoma cells that differentiate into neural cells. P19 cell clones overexpressing the three major forms of β-amyloid precursor protein from their cDNA constructs were established. Unlike a previous study in which P19-derived neurons had a limited α-secretase activity, all of these clones produced significant amounts of secreted β-amyloid precursor protein. When treated with retinoic acid, these transformed lines differentiated into neurons and survived better than did nontransformed parental P19 cells. Furthermore, P19-derived neurons survived better in medium conditioned by the transformed P19 line, and survival was reduced by immunoabsorption with an antibody to β-amyloid precursor protein. These results suggest neurotrophic effects of secreted β-amyloid precursor protein and contrast with a previous report in which overexpression of a full-length cDNA for β-amyloid precursor protein led to degeneration of P19-derived neurons. Western blot analysis suggested that this difference might result from different levels of expression of putative neurotoxic C-terminal fragments of β-amyloid precursor protein; moreover, P19-derived neurons differ from P19 stem cells in the processing of these C-terminal fragments.