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PubMed1980

Orientation of the hemes of high potential cytochromes relative to photosynthetic membranes, as shown by the linear dichroism of oriented preparations.

The orientations of high potential cytochromes with respect to photosynthetic membranes was investigated in spinach chloroplasts and in Rhodopseudomonas viridis. The general approach consists in detection with polarized light of photoinduced absorbance changes related to the oxidation of the cytochromes. The orientation of cytochrome c-558 was measured at room temperature in chromatophores and whole cells of Rps. viridis, oriented on glass slides and in a magnetic field, respectively. The orientation of cytochrome b-559 of green plants was detected at 77 K in magnetically oriented chloroplasts. In both cases the dichroic ratio for the alpha band shows that the heme plane makes an angle greater than 35 degrees C with the membrane plane. Moreover, the dichroic ratio is not constant throughout the alpha and beta bands, for both cytochrome c-558 and b-559. Linear dichroism spectra of oriented pure horse heart cytochrome c and cytochrome c2 of Rhodopseudomonas sphaeroides in stretched polyvinyl alcohol films show that the variations of the dichroic ratio in the alpha and beta bands can be explained by the occurrence of x- and y-polarized transitions absorbing at slightly different wavelengths.

Chloroplasts↗
PubMed1981

Cytochrome b oxidation and reduction reactions in the ubiquinone-cytochrome b/c2 oxidoreductase from Rhodopseudomonas sphaeroides.

1. The kinetics of cytochrome b reduction and oxidation in the ubiquinone-cytochrome b/c2 oxidoreductase of chromatophores from Rhodopseudomonas sphaeroides Ga have been measured both in the presence and absence of antimycin, after subtraction of contributions due to absorption changes from cytochrome c2, the oxidized bacteriochlorophyll dimer of the reaction center, and a red shift of the antenna bacteriochlorophyll. 2. A small red shift of the antenna bacteriochlorophyll band centered at 589 nm has been identified and found to be kinetically similar to the carotenoid bandshift. 3. Antimycin inhibits the oxidation of ferrocytochrome b under all conditions; it also stimulates the amount of single flash activated cytochrome b reductions 3- to 4-fold under certain if not all conditions. 4. A maximum of approximately 0.6 cytochrome b-560 (Em(7) = 50 mV, n = 1, previously cytochrome b50) hemes per reaction center are reduced following activating flashes. This ratio suggests that there is one cytochrome b-560 heme functional per ubiquinone-cytochrome b/c2 oxidoreductase. 5. Under the experimental conditions used here, only cytochrome b-560 is observed functional in cyclic electron transfer. 6. We describe the existence of three distinct states of reduction of the ubiquinone-cytochrome b/c2 oxidoreductase which can be established before activation, and result in markedly different reaction sequences involving cytochrome b after the flash activation. Poising such that the special ubiquinone (Qz) is reduced and cytochrome b-560 is oxidized yields the conditions for optimal flash activated electron transfer rates through the ubiquinone-cytochrome b/c2 oxidoreductase. However when the ambient redox state is lowered to reduce cytochrome b-560 or raised to oxidize Qz, single turnover flash induced electron transfer through the ubiquinone-cytochrome b/c2 oxidoreductase appears impeded; the points of the impediment are tentatively identified with the electron transfer step from the reduced secondary quinone (QII) of the reaction center to ferricytochrome b-560 and from the ferrocytochrome b-560 to oxidized Qz, respectively.

Bacteriochlorophylls↗
PubMed1983

A structural investigation of cytochrome c binding to photosynthetic reaction centers in reconstituted membranes.

Mammalian cytochrome c can effectively replace bacterial cytochrome c2 as the electron donor to the bacterial photosynthetic reaction center in either the natural chromatophore or a reconstituted reaction center/phospholipid membrane. In this paper, the reconstituted membrane was used to describe the nature of cytochrome c binding to the reaction center, the location of bound cytochrome c in the membrane profile and the perturbation of the reaction center and phospholipid profile structures indicated by cytochrome c binding. These structural studies utilized the combined techniques of X-ray and neutron diffraction.

Animals↗
PubMed1987

Oxidation of cytochrome c2 and of cytochrome c by reaction centers of Rhodospirillum rubrum and Rhodobacter sphaeroides. The effect of ionic strength and of lysine modification on oxidation rates.

The oxidation of cytochrome c2 by the photooxidized reaction center bacteriochlorophyll, P+-870, in chromatophores of Rhodospirillum rubrum can be described using second-order kinetics at all ionic strengths. In a system consisting of isolated R. rubrum reaction centers and purified R. rubrum cytochrome c2, the oxidation of cytochrome c2 also follows second-order kinetics. In both cases, the reaction rates at low ionic strength are weakly dependent on the ionic strength. The data suggest that the cytochrome remains mobile at very low ionic strength, since the observed kinetics can be easily explained assuming no significant tight binding of cytochrome c2 to the reaction center. In a system consisting of equine cytochrome c and reaction centers of either R. rubrum or Rhodobacter sphaeroides, the cytochrome c oxidation rate depends more strongly on the ionic strength. The high reaction rates at low ionic strength suggest that a significant portion of the cytochrome is bound. Using equine cytochrome c derivatives modified at specific lysine residues, it was shown that both R. rubrum and Rb. sphaeroides reaction centers react with equine cytochrome c through its exposed heme edge.

Bacteria↗
PubMed1988

Conversion of coupling factor 1 of Rhodospirillum rubrum from a Ca2+-ATPase into a Mg2+-ATPase.

Isolation of F1-ATPase from Rhodospirillum rubrum by chloroform extraction of chromatophores, followed by purification on a glycerol gradient, results in a very pure enzyme preparation containing five subunits with high Ca2+-ATPase activity (15 mumol per min per mg protein). Furthermore, conditions are reported under which the purified F1 exhibits Mg2+-dependent ATPase activity of about 35 mumol per min per mg protein. NaHCO3 stimulates the Mg2+-activity from 1.5 mumol per min per mg protein to 5 mumol per min per mg protein giving a maximal activity at a concentration of about 60 mM NaHCO3. Lauryl dimethylamine oxide (LDAO), octyl glucoside and nonanoyl N-methylglucamide enhance the Mg2+-ATPase activity from 1.5 to 14, 22 and 35 mumol per min per mg protein, respectively, in the absence of NaHCO3, and from 5 to 34, 30 and 37 mumol per min per mg protein, respectively, in the presence of 50 mM NaHCO3. The Vmax is increased, but the Km for ATP remains the same, about 0.22 mM, both in the absence of activators and in the presence of NaHCO3, LDAO or NaHCO3 plus LDAO. Ca2+-dependent ATPase activity is slightly stimulated by NaHCO3 but strongly inhibited by octyl glucoside.

Bicarbonates↗
PubMed1992

Pleiotropic effects of pufX gene deletion on the structure and function of the photosynthetic apparatus of Rhodobacter capsulatus.

By deletion of the pufX gene of Rhodobacter capsulatus from a plasmid carrying the puf operon and complementation of a chromosomal puf operon deletion, we created pufX mutants and used them to characterize possible functions of the pufX gene product. The pufX mutants were incapable of photosynthetic growth in a minimal medium, or in a rich medium at low light intensities, although second-site mutations suppressed this phenotype. Measurements made in vitro with intact and solubilized chromatophore preparations indicated that the individual complexes of the photosynthetic unit seemed to function normally, but electron transfer from the reaction center to the cytochrome b/c1 complex was impaired. The structures of the photosynthetic apparatus of pseudo-wild type and mutant strains were evaluated using absorption spectroscopy and electron microscopy. The pufX mutants had intracytoplasmic membrane invaginations about 50% larger in diameter than those of the pseudo-wild type and higher levels of B870 light-harvesting complex. It is concluded that the PufX protein plays an important role in the structure of the functional photosynthetic unit, and its absence results in loss of efficient electron transfer from the QB site of the reaction center to the Qz site of the cytochrome b/c1 complex.

Base Sequence↗
PubMed1992

Is bicarbonate in Photosystem II the equivalent of the glutamate ligand to the iron atom in bacterial reaction centers?

Photosystem II of oxygen-evolving organisms exhibits a bicarbonate-reversible formate effect on electron transfer between the primary and secondary acceptor quinones, QA and QB. This effect is absent in the otherwise similar electron acceptor complex of purple bacteria, e.g., Rhodobacter sphaeroides. This distinction has led to the suggestion that the iron atom of the acceptor quinone complex in PS II might lack the fifth and sixth ligands provided in the bacterial reaction center (RC) by a glutamate residue at position 234 of the M-subunit in Rb. sphaeroides RCs (M232 in Rps. viridis). By site-directed mutagenesis we have altered GluM234 in RCs from Rb. sphaeroides, replacing it with valine, glutamine and glycine to form mutants M234EV, M234EQ and M234EG, respectively. These mutants grew competently under phototrophic conditions and were tested for the formate-bicarbonate effect. In chromatophores there were no detectable differences between wild type (Wt) and mutant M234EV with respect to cytochrome b-561 reduction following a flash, and no effect of bicarbonate depletion (by incubation with formate). In isolated RCs, several electron transfer activities were essentially unchanged in Wt and M234EV, M234EQ and M234EG mutants, and no formate-bicarbonate effect was observed on: (a) the fast or slow phases of recovery of the oxidized primary donor (P+) in the absence of exogenous donor, i.e., the recombination of P+Q-A or P+Q-B, respectively; (b) the kinetics of electron transfer from Q-A to QB; or (c) the flash dependent oscillations of semiquinone formation in the presence of donor to P+ (QB turnover). The absence of a formate-bicarbonate effect in these mutants suggests that GluM234 is not responsible for the absence of the formate-bicarbonate effect in Wt bacterial RCs, or at least that other factors must be taken into account. The mutant RCs were also examined for the fast primary electron transfer along the active (A-)branch of the pigment chain, leading to reduction of QA. The kinetics were resolved to reveal the reduction of the monomer bacteriochlorophyll (tau = 3.5 ps), followed by reduction of the bacteriopheophytin (tau = 0.9 ps). Both steps were essentially unaltered from the wild type. However, the rate of reduction of QA was slowed by a factor of 2 (tau = 410 +/- 30 and 47 +/- 30 ps for M234EQ and M234EV, respectively, compared to 220 ps in the wild type).(ABSTRACT TRUNCATED AT 400 WORDS)

Benzoquinones↗
PubMed1994

Spectral alterations in Rhodobacter capsulatus mutants with site-directed changes in the bacteriochlorophyll-binding site of the B880 light-harvesting complex.

Site-directed mutagenesis has suggested that conserved histidine and alanine residues in the alpha-subunit of the B880 (LHI) antenna complex of Rhodobacter capsulatus (alpha His32 and alpha Ala28) form part of the bacteriochlorophyll binding site (Bylina, E.J., Robles, S.J. and Youvan, D.C. (1988) Isr. J. Chem. 28, 73-78). Spectroscopic characterization of chromatophores from alpha Ala28 mutants at 77 K revealed: (i) red shifts in B880 absorption and emission maxima of approximately 6 and 10 nm, respectively, with a serine exchange; (ii) red shifts of 3 nm with a glycine exchange; (iii) and no significant shifts with a cysteine exchange, despite a reduction of approximately 50% in B880 level. The strains with the serine and glycine exchanges showed characteristic fluorescence polarization increases over the red-edge of the B880 band, suggesting that the absorption red shifts arose from altered pigment-protein interactions rather than from increased oligomerization states that would be expected to show markedly diminished and red shifted rises in polarization (Westerhuis, W.H.J., Farchaus, J.W. and Niederman, R.A. (1993) Photochem. Photobiol. 58, 460-463). Excitation spectra of strains with alpha His32 to glutamine and alpha Ala28 to histidine exchanges, thought to be depleted in B880, revealed low levels of a 'pseudo-B880' complex with blue-shifted maxima and fluorescence polarization rises; when excited directly into this component, the former strain showed an emission spectrum similar to that of B880. An essentially wild-type electrochromic carotenoid response was observed only in the B880-containing mutants, since membranes isolated from the B880-depleted strains exhibited an increased permeability to ions.

Amino Acid Sequence↗
PubMed1987

Membrane adenosine triphosphatase in synchronous cultures of Rhodobacter sphaeroides.

Studies of intracytoplasmic membrane biogenesis utilizing synchronized cultures of Rhodobacter sphaeroides have revealed that most intracytoplasmic membrane proteins accumulate continuously throughout the cell cycle while new phospholipid appears discontinuously within the intracytoplasmic membrane. The resulting changes in the structure of the membrane lipids was proposed to influence the activities of enzymes associated with the intracytoplasmic membranes (Wraight, C.A., Leuking, D.R., Fraley, R.T. and Kaplan, S. (1978) J. Biol. Chem. 253, 465-471). We have extended the study of intracytoplasmic membrane biogenesis in R. sphaeroides to include the membrane adenosine triphosphatase. The membrane bound Mg2+-dependent, oligomycin-sensitive adenosine triphosphatase activity was measured throughout the cell cycle for steady-state synchronized cells of R. sphaeroides and found to accumulate discontinuously. Following treatment with an uncoupling reagent (2,4-dinitrophenol) the intracytoplasmic membrane associated adenosine triphosphatase activity was stimulated uniformly in membranes isolated at different stages of the cell cycle. The adenosine triphosphatase was also measured by quantitative immunoblots utilizing specific antibody to compare the enzyme activity and enzyme protein mass. Immunologic measurement of the adenosine triphosphatase in isolated membranes indicated a constant ratio of enzyme to chromatophore protein exists during the cell cycle in contrast to the discontinuous accumulation of adenosine triphosphatase activity. These results are discussed in light of the cell-cycle specific synthesis of the intracytoplasmic membrane.

Adenosine Triphosphatases↗
PubMed1984

HPLC purification of a biologically active membrane protein: the reaction center from photosynthetic bacteria.

Reaction centers from Rhodopseudomonas sphaeroides R 26 have been isolated from a crude extract obtained by lauryldimethylamine oxide extraction of chromatophore membranes, by HPLC using a combination of surface-mediated and size exclusion chromatography. The eluted RCs exhibit a normal activity (t 1/2 of the back-reaction is 70 ms) and are recovered in good yield (over 50% based on the activity) and purity (based on the A 280 nm/A 800 nm = 1.30 +/- 0.05 ratio and the characteristic 3 polypeptides SDS-PAGE pattern). The elution time (5-10 mn) is about two orders of magnitude faster than for the classical purification techniques.

Bacterial Proteins↗
PubMed1991

Immunological cross-reactivity between proton-pumping inorganic pyrophosphatases of widely phylogenic separated species.

Immunological cross-reactivity among three types of inorganic pyrophosphatases, that is, the proton pumping inorganic pyrophosphate synthase (H(+)-PPi synthase) and the soluble inorganic pyrophosphatase, both from Rhodospirillum rubrum, and the vacuolar membrane inorganic pyrophosphatase (H(+)-PPase) from mung bean (Vigna radiata), were examined by means of immunoblot analyses. Antibodies raised against the mung bean H(+)-PPase cross-reacted with the H(+)-PPi synthase from R. rubrum but not with the soluble PPase from R. rubrum. N,N'-dicyclohexylcarbodiimide (DCCD), which inhibits both synthesis and hydrolysis of PPi catalysed by purified and chromatophore H(+)-PPi synthase, binds to the enzyme as shown by fluorography of [14C]DCCD labelling. These results suggest that the R. rubrum H(+)-PPase share close structural similarities with the vacuolar H(+)-PPase from Mung bean.

Blotting, Western↗
PubMed1987

Localization of serotonin-immunoreactivity in the central nervous system of Octopus vulgaris by immunohistochemistry.

5-Hydroxytryptamine (5-HT, serotonin)-containing cells were localized in the central nervous system of Octopus vulgaris by use of the unlabelled peroxidase-antiperoxidase complex (PAP) immunohistochemical method employing highly specific antibodies to 5-HT present in paraformaldehyde-fixed tissue. Antibodies were raised in rabbits against an immunogen prepared by coupling 5-HT to bovine thyroglobulin (BTG) or to bovine serum albumin (BSA) with formaldehyde as the coupling reagent. The specificity of the immune reaction was studied by both absorption test and radioimmunoassay. The distribution of 5-HT immunoreactivity observed in octopus brain was essentially similar to that reported by other workers who used formaldehyde- or glyoxylic acid-induced fluorescence method. In addition, this immunohistochemical technique revealed 5-HT-containing perikarya in both the chromatophore and the palliovisceral lobes which were not detected by the previous fluorescence histochemical method. Thus, this immunocytochemical procedure appears to be a specific and very sensitive technique for the localization of 5-HT within the central nervous system of cephalopod Mollusca.

Animals↗
PubMed1991

Probing the primary quinone environment in photosynthetic bacterial reaction centers by light-induced FTIR difference spectroscopy.

The photoreduction of the primary electron acceptor, QA, has been characterized by light-induced Fourier transform infrared difference spectroscopy for Rb. sphaeroides reaction centers and for Rsp. rubrum and Rp. viridis chromatophores. The samples were treated both with redox compounds, which rapidly reduce the photooxidized primary electron P+, and with inhibitors of electron transfer from QA- to the secondary quinone QB. This approach yields spectra free from P and P+ contributions which makes possible the study of the microenvironment of QA and QA-.

Fourier Analysis↗
PubMed1991

Functional size analysis of pyrophosphatase from Rhodospirillum rubrum determined by radiation inactivation.

A radiation inactivation technique was employed to determine the functional size of pyrophosphatase (PPase) from the chromatophores of Rhodospirillum rubrum. The activities of hydrolysis and synthesis reactions of pyrophosphatase and its coupled proton translocation decayed in a simple exponential function with the increase of radiation dosages. D37 values of 5.2 +/- 0.7 and 5.8 +/- 0.8 Mrads were obtained for pyrophosphate hydrolysis and its associated proton translocation yielding molecular masses of 167.7 +/- 30.7 and 156.3 +/- 26.6 kDa, respectively. Similarly, a D37 value of 4.4 +/- 0.6 Mrads was measured for the acid-base induced pyrophosphate synthesis resulting in a radiation sensitive size of 196.3 +/- 31.9 kDa.

Hydrolysis↗
PubMed1991

Slow electrogenic events in the cytochrome bc1-complex of Rhodobacter sphaeroides. The electron transfer between cytochrome b hemes can be non-electrogenic.

The flash-induced formation of transmembrane electric potential differences (measured by carotenoid bandshift) and redox changes of cytochrome bh (b561) were monitored spectrophotometrically in Rb. sphaeroides chromatophores in a pH range from 7.5 to 10.0. It is shown that in the presence of antimycin A and at pH less than 8.3 the myxothiazol-sensitive, antimycin-insensitive component of the carotenoid bandshift is kinetically coupled to cytochrome bh reduction. The kinetics of both processes can be described by a single exponent with a rise time of about 10 ms. Alkalization of the medium (8.3 less than or equal to pH less than or equal to 9.2) causes the appearance of an additional constituent in this phase of the carotenoid response with the rise time varying in the range of 100-300 ms. With a further pH increase (pH greater than 9.2), the electrogenic constituent, kinetically linked to cytochrome bh reduction, diminishes. The obtained data are discussed within the framework of the scheme, assuming that the electron transfer between bl and bh hemes in the bc1 complex is, under certain conditions, accompanied by proton transfer in the same direction.

Antimycin A↗
PubMed1993

Structure and localization of mRNA encoding a pigment dispersing hormone (PDH) in the eyestalk of the crayfish Orconectes limosus.

The pigment-dispersing hormone (PDH) is produced in the eyestalks of Crustacea where it induces light-adapting movements of pigment in the compound eye and regulates the pigment dispersion in the chromatophores. To study this hormone at the mRNA level, we cloned and sequenced cDNA encoding PDH in the crayfish Orconectes limosus. The structure of the PDH preprohormone consists of a signal peptide, a PDH precursor-related peptide (PPRP) and the highly conserved PDH peptide at the carboxy-terminal end. In situ hybridization in combination with immunocytochemistry revealed four cell clusters expressing PDH in the optic ganglia of the eyestalk. Three clusters stained both with the PDH cRNA probe and the PDH antiserum, however, the perikarya in the lamina ganglionaris (LG) only stained with the PDH antiserum, suggesting the presence of a PDH-like peptide in the LG.

Amino Acid Sequence↗
PubMed1994

A specific carotenoid is required for reconstitution of the Rubrivivax gelatinosus B875 light harvesting complex from its subunit form B820.

The core light-harvesting complex B875 from Rubrivivax gelatinosus has been reconstituted from its subunit form B820 with hydroxyspheroidene, the carotenoid which is bound to native B875 antenna. Other carotenoids which are chemically similar to hydroxyspheroidene (spheroidene, spheroidenone, neurosporene and spirilloxanthin) gave only low levels of partial reconstitution. Absorption and circular dichroism spectra of the hydroxyspheroidene-containing, reconstituted B875 were identical with those of original B875 antenna isolated directly from chromatophores, indicating that the two hydroxyspheroidene molecules bind to their native sites within the (alpha beta)Bchl2 subunit during the reconstitution process. These observations point to a structural role for this carotenoid in determining the architecture of Rv. gelatinosus B875 antenna.

Binding Sites↗