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PubMed1989

Amount and turnover rate of the F0F1-ATPase and the stoichiometry of its inhibition by oligomycin in Rhodospirillum rubrum chromatophores.

The amount of F1-ATPase in chromatophores from Rhodospirillum rubrum was determined by Western blotting using anti-RrF1 rabbit antibodies. 9.1 mmol F1 (mol bacteriochlorophyll)-1 was obtained or 14% of the total protein content of the chromatophores. The turnover rate of the F0F1-ATPase was 17 molecules ATP s-1 during synthesis, 2 molecules ATP s-1 during hydrolysis under coupled conditions with Mg2+ as the divalent cation, and 7 molecules ATP s-1 during hydrolysis in the presence of carbonyl cyanide p-trifluoromethoxyphenylhydrazone. Binding of 1 mol oligomycin/mol F0F1-ATPase was found to inhibit the activities of the enzyme completely. A single binding site was found with a Kd of approximately 2 microM.

Adenosine Triphosphate↗

PubMed1987

Effects of exogenous guanosine on chromatophore differentiation in the axolotl.

Guanosine is shown to dramatically alter the pigment phenotype of axolotls by suppressing melanization and enhancing the biosynthesis and deposition of purine-derived pigments. Phenotypic changes caused by guanosine are manifested by altered chromatophore differentiation patterns such that few black pigment cells (melanophores) differentiate (and those that do are punctate and necrotic in appearance), whereas the development of yellow (xanthophore) and reflecting (iridophore) pigment cells is enhanced. Mechanisms for changes in chromatophore differentiation, and thus pattern formation, are discussed, including the possibility that pigment cells may undergo transdifferentiation in vivo.

Aging↗

PubMedDate not supplied

Dermal and epidermal chromatophores of the Antarctic teleost Trematomus bernacchii.

The physiological response and ultrastructure of the pigment cells of Trematomus bernacchii, an Antarctic teleost that lives under the sea ice north of the Ross Ice Shelf, were studied. In the integument, two types of epidermal chromatophores, melanophores and xanthophores, were found; in the dermis, typically three types of chromatophores--melanophores, xanthophores, and iridophores--were observed. The occurrence of epidermal xanthophore is reported for the first time in fish. Dermal melanophores and xanthophores have well-developed arrays of cytoplasmic microtubules. They responded rapidly to epinephrine and teleost melanin-concentrating hormone (MCH) with pigment aggregation and to theophylline with pigment dispersion. Total darkness elicited pigment aggregation in the majority of dermal xanthophores of isolated scales, whereas melanophores remained dispersed under both light and dark conditions. Pigment organelles of epidermal and dermal xanthophores that translocate during the pigmentary responses are carotenoid droplets of relatively large size. Dermal iridophores containing large reflecting platelets appeared to be immobile.

Animals↗

PubMed1993

Cytoskeletal architecture of dermal chromatophores of the freshwater teleost Oryzias latipes.

Cytoskeletal construction of dermal chromatophores of Oryzias latipes was studied by immunofluorescence microscopy. A microtubule system was most prominent in melanophores where a large number of microtubules emanated from the center of the cell. Xanthophores had an arrangement basically similar to that of melanophores, though the radial pattern became more irregular in the peripheral region where intersecting wavy microtubules were quite frequent. Oval-shaped leucophores exhibited the least-developed microtubule system, where the limited number of microtubules formed a loose basket-like architecture. Intermediate filaments were ubiquitously present in all types of chromatophores and were found to be vimentin-immunoreactive. Examination of doubly-labeled cells indicated that vimentin filaments had similar distribution patterns with microtubules. Orderly arranged bundles of actin filaments were found only in xanthophores, while in melanophores and xanthophores, actin expression was diffuse without displaying a conspicuous filamentous organization. Colchicine treatment induced depolymerization of microtubules and retraction of dendrites in varying degrees in cells in culture and in situ. Melanophores in culture are very sensitive to the treatment while xanthophores appeared to be more resistant in respect to the maintenance of cell morphology.

Actins↗

PubMed1999

The effect of temperature on the light-induced pigment movement in fish corneal chromatophores.

Corneal chromatophores of unusual morphology were used for studies on the influence of temperature on the intracellular pigment movement in two species of marine fish from different temperature zones: the tropical puffer, Canthigaster cinctus, and boreal whitespotted greenling, Hexagrammos stelleri. It was shown that both dispersion under bright illumination and aggregation at darkening are slower or decrease at lower temperatures when examined in the range of 12-27 degrees C. The mean speed of the pigment translocations in the individual cell process was 0.38 micron/s at the highest temperature examined, with a range of 0.17-1.0 micron/s. Near the middle of the temperature range, the dynamic characteristics of cell pigment movement in tropical and boreal species were rather close, suggesting that there would be little divergent adaptations with respect to the mechanisms of the pigment transport. Corneal chromatophores are considered as a new promising model for cell motility studies.

Animals↗

PubMed1983

Evidence for a glutamine synthetase-chromatophore association in the phototroph Rhodospirillum rubrum: purification, properties, and regulation of the enzyme.

The characteristics of soluble and membrane-bound glutamine synthetase (GS) from Rhodospirillum rubrum were compared with those of the enzyme located in situ (measured in detergent-treated cells). The results suggest that in vivo GS may be associated with, or bound to, the chromatophore membranes. GS was found to reversibly associate and dissociate from purified chromatophores as a function of the ionic strength of the buffer or the Mg2+ concentration. Solubilized GS was purified to homogeneity and found to be similar to the GS of enteric bacteria in that its molecular weight was about 600,000 and it had one type of subunit of 51,000 molecular weight. Removal of GS from the membrane had no effect on the Km values for the substrates of the biosynthetic reaction, but it did have a substantial effect on both its Mg2+ requirement (the Km increased 10-fold) and the sensitivity of the gamma-glutamyl transferase reaction to the inhibitor methionine sulfoximine (the I0.5 decreased from 1,500 to 60 microM). Both observations suggest that the active site of GS is influenced by its association with the membrane. GS activity was shown to respond to NH4+, phosphodiesterase, Mg2+, and adenylylation cofactors in a manner identical to that of the GS of the coliform bacteria, suggesting that the former may also respond to adenylylation and deadenylylation. Finally, R. rubrum GS was also inhibited by NH4+ by a newly observed, as yet undefined, system.

Bacterial Chromatophores↗

PubMed1999

Ultrastructural and biochemical analysis of epidermal xanthophores and dermal chromatophores of the teleost Sparus aurata.

We have studied the pigmentary system of the teleost Sparus aurata skin by electron microscopy and chromatographic analysis. Under electron microscopy, we found the dermis to contain the three major types of recognized chromatophores: melanophores, xanthophores and iridophores. Melanophores were more abundant in the dorsal region, whereas the iridophores were more abundant in the ventral region. The most important discovery was that of epidermal xanthophores. Epidermal xanthophores were the only chromatophores in the epidermis, something only found in S aurata and in a teleost species living in the Antartic sea. In contrast, the biochemical analysis did not establish any special characteristics: we found pteridine and flavin pigments located mostly in the pigmented dorsal region. Riboflavin and pterin were two of the most abundant coloured pigment types, but other colourless pigments such as xanthopterin and isoxanthopterin were also detected.

Animals↗

PubMed2006

Reconstruction of a kinetic model of the chromatophore vesicles from Rhodobacter sphaeroides.

We present a molecular model of a chromatophore vesicle from Rhodobacter sphaeroides. These vesicles are ideal benchmark systems for molecular and systemic simulations, because they have been well studied, they are small, and they are naturally separated from their cellular environment. To set up a photosynthetic chain working under steady-state conditions, we compiled from the experimental literature the specific activities and geometries that have been determined for their constituents. This data then allowed defining the stoichiometries for all membrane proteins. This article contains the kinetic part of the reconstructed model, while the spatial reconstruction is presented in a companion article. By considering the transport properties of the Cytochrome c(2) and ubiquinone pools, we show that their size and oxidation states allow for an efficient buffering of the statistical fluctuations that arise from the small size of the vesicles. Stoichiometric and kinetic considerations indicate that a typical chromatophore vesicle of Rb. sphaeroides with a diameter of 45 nm should contain approximately five bc(1) monomers.

ATP Synthetase Complexes↗

PubMed2006

A spatial model of the chromatophore vesicles of Rhodobacter sphaeroides and the position of the Cytochrome bc1 complex.

The photosynthetic apparatus of purple bacteria is generally considered a well-studied and understood system. However, recent atomic force microscopy images of flattened chromatophore vesicles from Rhodobacter sphaeroides restarted a debate about the stoichiometry and positions of the membrane proteins, with the interpretations of the observed images only partly being in agreement with earlier models. The most puzzling observation from the recent images is that the Cytochrome bc(1) complex, which is a central part of the photosynthetic apparatus, seems to be missing on the chromatophore vesicles, even when these were extracted from photosynthetically grown bacteria. From the available information on the geometry of the vesicle and of the proteins we reconstructed here a three-dimensional model vesicle at molecular resolution. Its central feature, also determining its diameter of approximately 45 nm, is an equatorial array of LH1 dimers, lined by a region of LH2 rings. This naturally puts the Cytochrome bc(1) complexes and the ATPase at the vesicle's poles. This spatial model may explain why the vesicle's endcaps with the bc(1) complexes are lost during the preparatory steps of the imaging process together with the ATPase and are therefore absent from the available images.

Adenosine Triphosphatases↗

PubMed2006

Ultrastructure of the dermal chromatophores in a lizard (Scincidae: Plestiodon latiscutatus) with conspicuous body and tail coloration.

Microscopic observation of the skin of Plestiodon lizards, which have body stripes and blue tail coloration, identified epidermal melanophores and three types of dermal chromatophores: xanthophores, iridophores, and melanophores. There was a vertical combination of these pigment cells, with xanthophores in the uppermost layer, iridophores in the intermediate layer, and melanophores in the basal layer, which varied according to the skin coloration. Skin with yellowish-white or brown coloration had an identical vertical order of xanthophores, iridophores, and melanophores, but yellowish-white skin had a thicker layer of iridophores and a thinner layer of melanophores than did brown skin. The thickness of the iridophore layer was proportional to the number of reflecting platelets within each iridophore. Skin showing green coloration also had three layers of dermal chromatophores, but the vertical order of xanthophores and iridophores was frequently reversed. Skin showing blue color had iridophores above the melanophores. In addition, the thickness of reflecting platelets in the blue tail was less than in yellowish-white or brown areas of the body. Skin with black coloration had only melanophores.

Animals↗

PubMed1978

Carotenoid and pterin pigment localization in fish chromatophores.

The classical sulfuric acid method for the histochemical detection of carotenoids has been adapted to give a reliable cytological localization of these compounds in fish chromatophores. This procedure consists mainly in fixing skin fragments in glutaraldehyde and dehydrating in a 50% solution of glycerin followed by exposure to air. It is essential that the preparation permit direct contact of the sulfuric acid with the pigment cells. Under these conditions, carotenoid containing cells stain green or blue. When associated with the extraction of the carotenoids by acetone, the procedure permits the distinction between pterin and carotenoid in fish chromatophores.

Acetone↗

PubMedDate not supplied

[Free radical centers in the chromatophores and preparations of Rhodospirillum rubrum reaction centers].

The light-induced free radical ESR signals in chromatophores and reaction center preparation of R. rubrum were studied. It has been shown that the properties of the signals in both systems were strictly identical. At the microwave powers higher than 10 mW the ESR signal at g approximatley 2.00 is saturated and its asymmetry arises. Changes of the ESR signal shape may be explained by the superposition of P870+ signal with that from the ubisemiquinone. Addition of ferricyanide to chromatophores induces in the dark a new ESR signal characterized by a linewidth of 4.5 Oe which presumably arises from the antenna bacteriochlorophyll aggregates, because this signal is absent in the reaction center preparations.

Bacterial Chromatophores↗

PubMed1979

[Shifts of the bacteriochlorophyll absorption band at 880 nm in chromatophores and subchromatophore pigment-protein complexes from Rhodospirillum rubrum].

The redox potential dependency of the light-induced absorption changes of bacteriochlorophyll in the chromatophores and subchromatophore particles from Rhodospirillum rubrum has been studied. The highest values of the absorption changes due to the bleaching of P870 and the blue shift of P800 are observed within the redox potential range of 360--410. At the potential values below 300 mV the 880 nm band of bacteriochlorophyll shifts to shorter wavelengths in the subchromatophore particles and to longer wavelengths in the chromatophores. Redox titration revealed that the red and blue shifts of 880 nm bacteriochlorophyll band are caused by the functioning of a non-identified component (X) which has an oxidation -- reduction midpoint potential close to 340 mV (n = 1) within the pH range of 6,0--7,6. The Em for this component decreases by 60 mV/pH unit within the pH range of 7.6--9,2. The results obtained suggest that the red shift is due to the transmembrane, while the blue shift -- to the local intramembrane electric field. The generation of both the transmembrane and local intramembrane electric fields apparently depends on redox transitions of the component X.

Bacterial Chromatophores↗

PubMed1972

Studies on the light-dependent synthesis of inorganic pyrophosphate by Rhodospirillum rubrum chromatophores.

Characteristics of inorganic pyrophosphate synthesis from inorganic orthophosphate were examined in chromatophores of Rhodospirillum rubrum. The application of an ADP-glucose pyrophosphorylase-trapping system has shown in an unequivocal fashion that pyrophosphate is a product of a light-dependent reaction utilizing P(i) as the substrate. Only very limited pyrophosphate synthesis takes place in the dark. The rates of synthesis of both ATP and pyrophosphate were studied under conditions in which the membrane-bound adenosine triphosphatase and pyrophosphatase activities would normally make these substances unstable. The maximum rate of pyrophosphate synthesis was 25% of that for ATP synthesis, with maximum activation of pyrophosphate synthesis occurring at a lower light-intensity than that required for ATP synthesis. As a result, at low light-intensity the rate of pyrophosphate formation approached that of ATP. Maximal rates of synthesis of both pyrophosphate and ATP were attained only on the addition of an exogenous reducing agent. Conditions for optimum pyrophosphate synthesis required about one-half of the concentration of the reductant required for maximum ATP synthesis. Consistent with previous reports, oligomycin inhibited ATP synthesis, but had little influence on the rate of pyrophosphate synthesis. In membrane particles that retained pyrophosphatase activity but were treated to remove adenosine triphosphatase activity and the ability to photophosphorylate ADP, oligomycin stimulated light-dependent pyrophosphate synthesis by nearly 250%. The influence of Mg(2+) concentration, pH and various inhibitors and uncouplers on pyrophosphate synthesis was studied. The results are discussed with respect to the mechanism and function of electron-transport-coupled energy conservation in R. rubrum chromatophores.

Adenosine Diphosphate↗

PubMedDate not supplied

[Effect of dehydration on electron transport from membrane-bound cytochromes c to bacteriochlorophyll of the photosynthetic reaction center in chromatophores of purple thiobacteria].

A method is proposed for spectroscopic probing photo-induced reversible oxidation-reduction changes of high-potential cytochrome in chromatophore films of various humidity. On these preparations of Ect. shaposhnikovii and Chr. minutissium it was found that the characteristic time of cytochrome oxidation, tau, in samples with a high degree of humidity (P/Ps = 0.75) is 2-3 mus, which is close to that seen under physiological conditions (a suspension of intact cells or chromatophores). It was found that under continuous or pulsed illumination the lowering of the relative humidity from 0.75 to 0.15 P/Ps results in a reversible decrease in the amount of cytochrome molecules that can undergo photooxidation. The fraction of cytochrome pool that retains its activity shows a rate of oxidation which remains almost without change. The observed hydration effect and its involvement in the control of the photo-induced oxidation of cytochromes must be taken into account when a model of the molecular mechanism of this process is constructed on the basis of the electron tunneling theory. It is also shown that the dark-reduction kinetics of high-potential cytochrome consist of two components: a fast component with t1/2 = 1-3s which is independent of the sample humidity and a slow component with t1/2 = 5-20 s whose lifetime increases by a factor of 3-5 on reducing the humidity. At a high degree of humidity (P/Ps = 0.75-0.5), the kinetics of cytochrome dark-reduction exhibits only the slow component. The fast component is probably associated with the return of an electron from the primary ferroquinone acceptor and the slow component seems likely to be due to the direct transfer of an electron from exogenous electron donor to the cytochrome.

Bacterial Chromatophores↗

PubMedDate not supplied

[Mössbauer spectroscopy of intramolecular mobility in chromatophores from Rhodopseudomonas spheroides].

Mobility of the Mössbauer label attached to the membrane proteins and the Mössbauer probe embedded into the lipid matrix of the bacterial chromatophores were studied. Positive correlation was established between the dynamic properties of hydrophobic compartments in the chromatophores and functional electron--transport activity at the level of quinone cofactors associated with the photosynthetic reaction centres.

Bacterial Chromatophores↗

PubMed1981

[Role of cofactors in membrane potential generation by Rhodospirillum rubrum chromatophores incorporated in a teflon filter].

The chromatophores of the bacterium Rhodospirillum rubrum were incorporated into a Teflon filter impregnated with a decane solution of phospholipids and the light-induced electric potential difference (delta psi) between the aqueous phases separated by the filter was measured. The generation of delta psi in such a system at continuous light requires the presence of cofactors, i. e. artificial electron donors and acceptors. These cofactors provide for a steady-state flow of e by regenerating the reduced form of the photo-oxidized reaction center bacteriochlorophyll and by reoxidizing the photo-reduced quinone acceptor of the reaction center. The most efficient donors are the reduced forms of nitrogen-containing redox mediators, e. g. TMPD, DAD, PMS, DCPIP and methylene blue, while p-benzoquinones with E07' approximately greater than 150 mV are practically inactive. The oxidized forms of nitrogen-containing mediators and a wide variety of p-quinones with E07' down to -220 mV can be used as electron acceptors. Using inhibitor analysis and compounds with different E0' it is shown that the cofactors donate electrons immediately to the reaction center bacteriochlorophyll and accept them from a low potential deprotonated form of the primary acceptor QI, substituting the secondary acceptor QII. The inability of hydrophilic sulfonate-substituted quinones to act as acceptors suggests that QI cannot be localized on the outer surface of the chromatophores.

Bacterial Chromatophores↗

PubMed1980

[Effect of cobalt and copper o-phenanthroline complexes on electron transport and energy coupling activity in reaction centers and chromatophores of purple bacteria].

The effects of cobalt and copper o-phenanthroline complexes on electron transfer and energy coupling activity in the reaction center and chromatophore preparations of purple bacteria were studied. In terms of their effects on the systems under study these complexes fall into two groups, i.e. cobalt complexes with a high electron transfer activity, which stimulate membrane energization, and copper complexes which contribute to the chromatophore membrane deenergization. Among a variety of complexes studied the perchlorate tris-o-phenanthroline complex Co(II) and the chloride 4,7-diphenyl-o-phenanthroline complex Cu(II) were found to have the highest activity. Both cobalt and copper o-phenanthroline complexes may be a promising tool for regulating bioenergetic processes.

Bacterial Chromatophores↗