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PubMed1985

Photoaffinity labeling of an antimycin-binding site in Rhodopseudomonas sphaeroides.

Tritium-labeled 3-azidosalicyl-N-(n-octadecyl)amide was synthesized and used as a photoaffinity probe for the antimycin-binding site in both purified ubiquinone-cytochrome b-c1 oxidoreductase and chromatophore vesicles from the photosynthetic bacterium Rhodopseudomonas sphaeroides. In both systems, a prominently labeled protein had a molecular weight of 11,000. Binding to this protein was inhibited by preincubation of the reaction mixture with antimycin prior to addition of the radioactive analog and subsequent irradiation. The antimycin analog, 3-azidosalicyl-N-(n-octadecyl)amide, inhibited succinate-cytochrome c reductase activity in chromatophore vesicles by 50% at a concentration of 150 nmols/mg of protein.

Affinity Labels↗

PubMed1988

Comparative strategies of pigmentary regulation in invertebrates.

This brief survey of color change strategies among invertebrates has dealt mainly with the diversity encountered in three aspects of their pigment cell biology: (1) the types of chromatophores they possess, (2) the control of color changes by nerves or hormones if the chromatophores are not acting only as independent effectors and (3) the functions of the physiological color changes these animals exhibit. Of these three topics, much less is known about the last one, the functions of the color changes, than about the first two. There has been much hypothesizing about the functions of color changes and the advantages such changes presumably confer, but relatively few data have been generated to support the hypotheses.

Animals↗

PubMed1993

ATPase of Rhodospirillum rubrum requires three functional copies of beta subunit as determined by radiation inactivation analysis.

Radiation inactivation analysis yielded a functional unit of 170 +/- 26 kDa as beta subunit of ATPase was irradiated and then reconstituted to beta-depleted chromatophores of Rhodospirillum rubrum. A functional size of 132 +/- 17 kDa for the beta-depleted ATPase moiety involved in ATP hydrolysis reaction was also determined. When both purified beta subunit and beta-depleted chromatophore were irradiated separately, reconstituted, and then activity measured, the functional mass was 312 +/- 50 kDa. Our compelling evidence directly indicates that three functional copies of beta subunits were required for ATP hydrolysis.

Adenosine Triphosphatases↗

PubMed1996

Cellular signalling in vertebrate pigment cells.

Chromatophores are specialized integumental stellate cells that synthesize and store pigments. Pigment granules are translocated within chromatophores of poikilothermic vertebrates and crustaceans in response to photic, thermal and/or neurohormonal stimuli, allowing the animal to rapidly change color for thermoregulation, adaptation to light and background, and social behavior display. Birds and mammals do not show color changes, but may present slow long-term responses, such as melanocyte proliferation, melanin synthesis and melanin granule translocation into feathers, hair and surrounding keratinocytes. Pigment translocation in lower vertebrates as well as pigment production in all vertebrates are modulated by a variety of hormones and neurotransmitters acting on transmembrane receptors located on the cell surface. Alpha-melanocyte-stimulating hormone (alpha-MSH), melanin-concentrating hormone (MCHA), melatonin and catecholamines are the most important pigment cell agonist in vertebrates. The major signalling pathway leading to pigment dispersion and melanin synthesis appears to be involve stimulation of adenylate cyclase followed by an increase in the cAMP level and activation of cAMP-dependent protein kinases (PKAs). Another melanogenesis-related intracellular pathway involves the activation of protein kinase C (PKC) by diacylglycerol, and the increase in cytosolic Ca2+ by inositol triphosphate. Growth factors such as basic fibroblast growth factor (bFGF), hepatocyte growth factor (HGF) and mast cell growth factor (MGF or KIT ligand), and UV radiation modulate the melanogenic and mitogenic processes in vertebrate melanocytes as well.

Adaptation, Physiological↗

PubMed1999

Expression and one-step purification of a fully active polyhistidine-tagged cytochrome bc1 complex from Rhodobacter sphaeroides.

The fbcB and fbcC genes encoding cytochromes b and c1 of the bc1 complex were extended with a segment to encode a polyhistidine tag linked to their C-terminal sequence allowing a one-step affinity purification of the complex. Constructions were made in vitro in a pUC-derived background using PCR amplification. The modified fbc operons were transferred to a pRK derivative plasmid, and this was used to transform the fbc- strain of Rhodobacter sphaeroides, BC17. The transformants showed normal rates of growth. Chromatophores prepared from these cells showed kinetics of turnover of the bc1 complex on flash activation which were essentially the same as those from wild-type strains, and analysis of the cytochrome complement and spectral and thermodynamic properties by redox potentiometry showed no marked difference from the wild type. Chromatophores were solubilized and mixed with Ni-NTA-Sepharose resin. A modification of the standard elution protocol in which histidine replaced imidazole increased the activity 20-fold. Imidazole modified the redox properties of heme c1, suggesting ligand displacement and inactivation when this reagent is used at high concentration. The purified enzyme contained all four subunits in an active dimeric complex. This construction provides a facile method for preparation of wild-type or mutant bc1 complex, for spectroscopy and structural studies.

Amino Acid Sequence↗

PubMed1985

Regulation of nitrogenase activity by covalent modification in Chromatium vinosum.

Nitrogenase in Chromatium vinosum was rapidly, but reversibly inhibited by NH4+. Activity of the Fe protein component of nitrogenase required both Mn2+ and activating enzyme. Activating enzyme from Rhodospirillum rubrum could replace Chromatium chromatophores in activating the Chromatium Fe protein, and conversely, a protein fraction prepared from Chromatium chromatophores was effective in activating R. rubrum Fe protein. Inactive Chromatium Fe protein contained a peptide covalently modified by a phosphate-containing molecule, which migrated the same in SDS-polyacrylamide gels as the modified subunit of R. rubrum Fe protein. In sum, these observations suggest that Chromatium nitrogenase activity is regulated by a covalent modification of the Fe protein in a manner similar to that of R. rubrum.

Ammonia↗

PubMed1996

The effect of different levels of the B800-850 light-harvesting complex on intracytoplasmic membrane development in Rhodobacter sphaeroides

A role for the peripheral (B800-850) light-harvesting complex in vesicularization of the Rhodobacter sphaeroides intracytoplasmic membrane (ICM), suggested from studies in mutant strains lacking one or more of the pigment-protein complexes, was examined further in the wild-type strain NCIB 8253 grown at high ( approximately 1000 W m-2), moderate ( approximately 300 W m-2), and low ( approximately 100 W m-2) light intensities. The resulting ICM vesicles (chromatophores) had B800-850 levels related inversely to irradiance and banded in rate-zone sedimentation at approximately 1.10, 1.09, and 1.07 g ml-1, respectively. Equilibrium centrifugation on iso-osmotic gradients indicated that this distinct sedimentation behavior resulted solely from differences in hydrodynamic radii. These size differences were confirmed by gel-exclusion chromatography and in electron micrographs of thin-sectioned cells. A pulse-chase study of ICM growth following a tenfold reduction in light intensity showed a relatively slow equilibration of membrane proteins during adaptation, and that new protein was incorporated largely into additional ICM formed at the lowered illumination level, giving rise to chromatophores of reduced size and elevated B800-850 content. These results provide further evidence for a model in which the B800-850 complex both drives development of vesicular ICM in Rba. sphaeroides and determines the size of resulting vesicles.

Journal Article↗

PubMed1996

Regulation of the Expression of the Photosynthetic Apparatus of Rhodobacter capsulatus Grown in Nitrogen-Limited Chemostat Cultures

Rhodobacter capsulatus was grown in chemostat cultures under different dilution rates and with ammonium ions as the limiting nutrient. The maximal growth rate (μmax) and the Monod cell growth saturation coefficient (Ks), were calculated from batch cultures grown at different concentrations of NH4+. The experiments in chemostat were carried out at 0.25 mM (NH4)2SO4, and the dilution rates were varied between 38% and 75% of μmax. The results indicated that under continuous culture conditions the cell yield coefficient (Y) (mg dry weight x μmol consumed ammonium sulfate-1) decreased with increasing dilution rate (D). On the contrary, the cell yield was constant when expressed as mg cellular protein x μmol consumed ammonium sulfate-1. This occurred as a consequence of both an increase in the consumed ammonium sulfate and a simultaneous decrease in the cell biomass production at increasing growth rates. The cells produced at higher growth rates had a higher protein content per cell. The specific content of bacteriochlorophyll (Bchl) decreased (between 3 and 4 times) with increasing growth rates measured in either cells or chromatophores. However, the absorption spectra of the cells indicated that the ratio LHI (light-harvesting complex I) to LHII (light-harvesting complex II) Bchl complexes did not change. The reaction center (RC) complex content varied in parallel with the total Bchl content, yielding a constant photosynthetic unit of 65 mol Bchl x mol RC-1 at different Ds. On the other hand, the uncoupled ATPase-specific activity measured in chromatophores was usually between 30% and 40% higher at the highest growth rates reached in these experiments.

Journal Article↗

PubMed1977

Reconstituted energy transfer from antenna pigment-protein to reaction centres isolated from Rhodopseudomonas sphaeroides.

Efficient energy transfer has been reconstituted between an antenna pigment-protein and reaction centres isolated from the photosynthetic membrane of Rhodopseudomonas sphaeroides. The reconstituted system has fluorescence induction kinetics and fluorescence yields similar to those obtained from antenna bacteriochlorophyll in chromatophores. The results indicated that closed reaction centres quench fluorescence from the antenna pigment-protein, although not as strongly as photochemically active reaction centres. The measurement of fluorescence yields from chromatophores of the reaction centreless mutant PM-8 and of the parent strain Ga confirmed these observations. The fluorescence yield from the reconstituted system was approximately the same whether the reaction centres had been closed by photo-oxidation of the bacteriochlorophyll electron donor or chemical reduction of the primary acceptor, indicating a similar lifetime for the excited singlet state in both states of the reaction centres.

Bacteriochlorophylls↗

PubMed1977

Necessity of a membrane component for nitrogenase activity in Rhodospirillum rubrum.

Acetylene reduction catalyzed by nitrogenase from Rhodospirillum rubrum has low activity and exhibits a lag phase. The activity can be increased by the addition of a chromatophore membrane component and the lag eliminated by preincubation with this component, which can be solubilized from chromatophores by treatment with NaCl. It is both trypsin- and oxygen-sensitive. Titration of the membrane component with nitrogenase and vice versa shows a saturation point. The membrane component interacts specifically with the Fe protein of nitrogenase, the interaction being ATP- and Mg2+-dependent.

Adenosine Triphosphate↗

PubMed1979

Characterisation of reaction centers and their phospholipids from Rhodospirillum rubrum.

1. Reaction centers from Rhodospirillum rubrum have been extracted with the zwitterionic detergent lauryl dimethyl amine oxide. Subsequent purification has been achieved by gel filtration and ion-exchange chromatography. The pure reaction centers are composed of three protein subunits (L, M, H), bacteriocholorophyll and bacteriopheophytin in the ratio 2 : 1 and phospholipids. 2. The phospholipid composition has been found to be similar to that of whole chromatophore membrane, except that diphosphatidyl glycerol is present in higher amount in the isolated complex. When the detergent treatment of the chromatophore membrane is done in the presence of NaCl, a lower phospholipid content in isolated reaction centers has been found together with a lower stability in the association among the protein subunits. In this complex, the largest subunit H is easily split off and a LM complex is obtained. It is concluded that the phospholipids play an important role in the stability of reaction center complexes.

Bacterial Proteins↗

PubMed1981

The inhibition of photosynthetic electron transfer in Rhodospirillum rubrum by N ,N' -dicyclohexylcarbodiimide.

N ,N' -Dicyclohexylcarbodiimide (DCCD) at concentrations above 0.1 mM inhibits light-induced generation of a membrane potential in the course of cyclic and non-cyclic electron transfer, as well as light-induced oxygen uptake due to interaction of photoreduced secondary (loosely bound) ubiquinone with O2 in Rhodospirillum rubrum chromatophores. Similarly to o-phenanthroline, DCCD blocks the electron transfer in the chromatophores between the primary (tightly bound) and secondary ubiquinones.

Carbodiimides↗

PubMed1990

The role of c-type cytochromes in the photosynthetic electron transport pathway of Rhodobacter capsulatus.

(1) Short flash excitation of membrane vesicles of a cytochrome-c2-deficient mutant of Rhodobacter capsulatus (strain MT-G4/S4) led to rapid oxidation of a c-type cytochrome. In redox titrations, the photooxidation of c-type cytochrome was attenuated with a midpoint of approx. +360 mV. Vesicles from a control strain, MT1131, gave similar results. These findings are consistent with those of Prince et al. (Prince, R.C., Davidson, E., Haith, L.E. and Daldal, F. (1986) Biochemistry 25, 5208-5214). (2) In anaerobic intact cells the extent of rapid re-reduction of c-type cytochrome oxidised after a flash was less in MT-G/S4 than in MT1131. Cytochrome c reduction in both strains was inhibited by myxothiazol. The myxothiazol-sensitive component of the electrochromic absorbance change in cells indicated that rapid charge separation through the cytochrome bc1 complex was less extensive after a flash in MT-G4/S4 than in MT 1131. (3) In anaerobic intact cells and in chromatophores of Rb. capsulatus strain MT-GS18, a mutant deficient in both cytochrome c1 and cytochrome c2, flash excitation led to the oxidation of c-type cytochrome. Redox titrations and spectra of chromatophores suggested that this is the same cytochrome as was photooxidized in vesicles of MT-G4/S4 and MT1131. This result is in contrast with earlier findings (Prince, R.C. and Daldal, F. (1987) Biochim. Biophys, Acta 894, 370-378) in which it was reported that no photooxidation of c-type cytochrome occurred in the absence of c1 and c2, and argues against the possibility that cytochrome c1 can rapidly and directly donate electrons to the reaction centre. (4) It is proposed that a previously uncharacterized, membrane-bound c-type cytochrome (Em7 approximately +360 mV) is present in Rb-capsulatus MT1131, in the c2-deficient mutant MT-G4/34 and in the c1/c2-deficient mutant MTGS18. This cytochrome and cytochrome c2 are alternative electron donors to the reaction centre in strain MT1131.

Cytochrome c Group↗

PubMed1993

Electrochromic responses of carotenoid absorbance bands in purified light-harvesting complexes from Rhodobacter capsulatus reconstituted into liposomes.

Light-Harvesting Complexes I and II (LHI and LHII) were extracted from chromatophores of Rhodobacter capsulatus, purified in Triton X-100 and reconstituted into phospholipid vesicles. Application of membrane potentials (K+ diffusion potentials) to LHII proteoliposomes led to absorbance changes in the carotenoid bands which were spectrally similar to those in chromatophores. These (electrochromic) absorbance changes were linear with the applied membrane potential between -107 mV and +105 mV. The data were consistent with the existence of two forms of carotenoid in LHII. One form, comprising 2/3 of the total and with a long wavelength absorbance maximum at 510 nm, was not significantly affected by membrane potential. The other component, comprising 1/3 of the total and with a long wavelength absorbance maximum at 516.5 nm, was shifted by approx. 1.6 nm to the red by a membrane potential of 105 mV. Reduction of the B800 bacteriochlorophyll in LHII with NaBH4 before reconstitution did not affect the absorbance spectrum of the carotenoids and it did not affect their response to applied membrane potentials in proteoliposomes. Although the electrochromically-sensitive carotenoids might be associated with B800, interactions with the bacteriochlorophyll are perhaps not the cause of the polarisation of the carotenoid that is responsible for the linearity of the response. The carotenoids in reconstituted LHI complexes were not detectably electrochromic. The electrochromic absorbance changes of carotenoids in LHII could be useful for membrane potential measurement in liposomes containing ion-translocating proteins.

Bacterial Proteins↗

PubMed1978

The properties of hydrogenase from Thiocapsa roseopersicina.

The soluble and chromatophore-bound hydrogenases from the purple sulphur bacterium Thiocapsa roseopersicina strain BBS were purified up to homogeneity and the properties studied. The amino acid composition of hydrogenase preparations from different fractions of T. roseopersicina is identical, glycine and alanine as N-terminal amino acid residues. In comparison with other hydrogenases, especially in the immobilized state, the preparations obtained are shown to be more stable to O2 during storage and they are characterized by high thermal stability. Inactivation is observed above 78--80 degrees C and the optimal temperature for enzyme action is 70 degrees C. The homogeneous enzyme preparations catalyse the exchange reaction between 2H2 and H2O and reversible redox reactions of methyl viologen and benzyl viologen as well as H2 formation from reduced ferredoxin. According to our data, the hydrogenase of T. roseopersicina bound with chromatophores is identical to the soluble one.

Amino Acids↗

PubMed1992

Isolation and characterisation of a functional alpha beta heterodimer from the ATP synthase of Rhodospirillum rubrum.

An alpha beta heterodimer of the F1-ATPase of Rhodospirillum rubrum was isolated by extraction of chromatophores with LiCl. Each alpha beta heterodimer contains one tightly bound ADP, which is released upon removal of medium Mg2+. The dimer can be reversibly dissociated by removal of Mg(2+)-ions. The alpha beta heterodimer restores both ATP-synthetic and -hydrolytic activities to LiCl-treated chromatophores, saturation being achieved at approximately 2 mmol alpha beta.mol BChl-1. The heterodimer itself hydrolyses Mg-ATP with an activity distinct from RF1, being unaffected by azide or sulphite ions. The Vmax and Km (ATP) for this Mg(2+)-dependent activity were 110 +/- 10 nmol.min-1.mg protein-1 and 100 +/- 30 microM, respectively. The Km did not differ significantly from that of RF1.

Amino Acid Sequence↗

PubMed2006

Spectral and kinetic resolution of the bc1 complex components in situ: a simple and robust alternative to the traditional difference wavelength approach.

The kinetics of the cytochrome (cyt) components of the bc(1) complex (ubiquinol: cytochrome c oxidoreductase, Complex III) are traditionally followed by using the difference of absorbance changes at two or more different wavelengths. However, this difference-wavelength (DW) approach is of limited accuracy in the separation of absorbance changes of components with overlapping spectral bands. To resolve the kinetics of individual components in Rhodobacter sphaeroides chromatophores, we have tested a simplified version of a least squares (LS) analysis, based on measurement at a minimal number of different wavelengths. The success of the simplified LS analysis depended significantly on the wavelengths used in the set. The "traditional" set of 6 wavelengths (542, 551, 561, 566, 569 and 575 nm), normally used in the DW approach to characterize kinetics of cyt c(tot) (cyt c(1)+cyt c(2)), cyt b(L), cyt b(H), and P870 in chromatophores, could also be used to determine these components via the simplified LS analysis, with improved resolution of the individual components. However, this set is not sufficient when information about cyts c(1) and c(2) is needed. We identified multiple alternative sets of 5 and 6 wavelengths that could be used to determine the kinetics of all 5 components (P870 and cyts c(1), c(2), b(L), and b(H)) simultaneously, with an accuracy comparable to that of the LS analysis based on a full set of wavelengths (1 nm intervals). We conclude that a simplified version of LS deconvolution based on a small number of carefully selected wavelengths provides a robust and significant improvement over the traditional DW approach, since it accounts for spectral interference of the different components, and uses fewer measurements when information about all five individual components is needed. Using the simplified and complete LS analyses, we measured the simultaneous kinetics of all cytochrome components of bc(1) complex in the absence and presence of specific inhibitors and found that they correspond well to those expected from the modified Q-cycle. This is the first study in which the kinetics of all cytochrome and reaction center components of the bc(1) complex functioning in situ have been measured simultaneously, with full deconvolution over an extended time range.

Electron Transport Complex III↗

PubMed1991

Langmuir-Blodgett monolayer films of the Rhodopseudomonas viridis reaction center: determination of the order of the hemes in the cytochrome c subunit.

The Langmuir-Blodgett (LB) film technique has been applied to produce oriented and photo-active films of isolated reaction center cytochrome c complexes (RC-cyt c) and chromatophore membranes from the photosynthetic bacterium Rhodopseudomonas viridis. Linear dichroism (LD) and redox potentiometry have been used to identify the four cytochrome c hemes of the RC-cyt c complex. Resolved angular orientations of the four hemes in LB films of both isolated RC-cyt-c complexes and of chromatophore membranes permit the reduction of the 24 possible arrangements to two. Additional structural and functional information from other sources allows us to propose a model which best accounts for all the available experimental data.

Cytochrome c Group↗