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PubMed1982

A sensitive and rapid method for determination of pyrophosphatase activity.

A new, rapid and sensitive method of measuring the rate and amount of PPi hydrolysis is described. The method is based on registration of small pH changes, caused by decrease of hydrogen-ion concentration during the pyrophosphatase reaction. With this detected value of hydrogen-ion concentration change and the buffering capacity of each reaction mixture determined by titration, the rate and amount of PPi hydrolysis can be calculated. The results obtained by pH method are in good agreement with values determined by direct phosphate analysis. The described method can be applied to the continuous determination of pyrophosphatase activity in chromatophores, mitochondria, crude extracts or purified enzymes.

Bacterial Chromatophores↗

PubMed1976

[Coloring cells of the cornea of trout].

Cells from the eye cornea of Hexagrammos octagrammus which are responsible for changes of the cornea colour from bright orange to colourless, depending on the light conditions, are described. It was shown that the change in cornea colour was due to a shift of red pigment from the cell body into its processes (in the light) and in the opposite direction at the dark adaptation of animals. The ultrastructural constitution of these cells has a number of characteristics. The whole cell cytoplasm is filled up with fine lipid droplets wherein carotenoid pigments giving red colour to these cells are presumably dissolved; the cytoplasmic membrane forms numerous deep and branched folds into the cell and has a lot of pinocytose visicles; the cell body and especially the process display many microtubes arranged regularly. The described cells differ greatly in their form, size and ultrastructural constitution from the known types of pigment cells (melanophores, xanthophores and erythrophores). This makes it possible to consider them as chromatophores of an independent type.

Animals↗

PubMedDate not supplied

[Possible role of macromolecular components in the functioning of photosynthetic reaction centers of purple bacteria].

The temperature dependencies of the photoconversion of pigments P870--P890 were studied using isolated chromatophores and photosynthetic reaction centres (RC's) of purple bacteria. The samples were prepared by extraction with organic solvents (light petroleum and a combination of light petroleum and methanol) and modified through cross-linking the functional groups of proteins by treatment with glutaraldehyde or denatured by various physical and chemical treatments. The data provide further evidence that the pool of RC secondary acceptors is formed by the compounds of quinone nature located in the hydrophobic surrounding. Similar molecules localized in a more polar medium act as primary acceptors. The findings indicate on the essential role of macromolecular components in the RC's functioning and also suggest that the photochemical charge separation is conformation-controlled.

Bacterial Chromatophores↗

PubMedDate not supplied

[Ultrastructure of Thiocapsa roseopersicina under various cultivation conditions].

The cells of the purple sulphur bacterium Thiocapsa roseopersicina, strain BBS, growing in the light and in the darkness, contain chromatophores of the normal vesicular type. The amount and dimensions of the vesicules in the cells depend on the composition of the medium and the conditions of cultivation. During anaerobic growth of the bacterium in the light in the medium with pyruvate, large cells appear with complicate invaginations of the cytoplasmic membrane. The cells may contain, besides drops of sulphur, polyphosphates, and poly-beta-hydroxybutyric acid, spherical inclusions of a fine-grain structure.

Aerobiosis↗

PubMedDate not supplied

[Conformational mobility and functional activity of photosynthetic reaction centers of Rhodopseudomonas sphaeroides].

In pigment-protein complexes of photosynthetic reaction centres (RC's), extracted from chromatophore membranes of Rps. sphaeroides with sodium dodecylsulphate, functional activity and intramolecular mobility were studied as a function of temperature and hydration by use of the technique of optical absorbance and ESR spectroscopy. Over the studied temperature range from +20 to -120 degrees C and at a relative humidity (P/Ps) from 0.9 to 0.1, there observed a close interrelationship between reversible kinetic changes of direct and backward redox-reactions of the photo-reduced endogeneous acceptor of quinone nature and the effective parameter of the correlation time of the rotational diffusion of the hydrophobic spin probe as well as of spin labels chemically bound to SH- and COOH-groups of amino acid residues of the RC's protein. The findings support the view that the conformational dynamics in the RC controls the effectiveness of the primary processes of stabilization of photochemically separated charges.

Bacterial Chromatophores↗

PubMed1979

[Electron acceptors in photosynthetic reaction centers from Rhodopseudomonas spheroides].

Using optical differential spectroscopy and EPR, a parallel study of light-induced electron transfer between the primary (X1) and secondary (X2) quinone-like acceptors in the preparations of reaction centers (RC) isolated from bacterial chromatophore membranes with sodium dodecyl sulfate was carried out. The data from direct measurements of the rate constant temperature dependence for the interaction between light-reduced X1 and X2 (KX1X2) are in good agreement with the data calculated from the kinetic analysis of dark reduction of photooxidized bacteriochlorophyll RC on the acceptors X1 and X2 (KX1X2 = 2.10(-1)S at 20 degrees; Ea = 11,8 kcal.mol-1 within the temperature range of 20 degrees-- -20 degrees). This evidence proves the efficiency of the previously used approach /1, 2/ for the evaluation of the X1-X2 interaction. The method proposed was used for a kinetic analysis of a low-temperature electron transfer from X1 to X2 in RC isolated with lauryldimethylaminoxide (KX1X2 = 2,3.10(2) S-1 at 20 degrees; Ea = 5,5 kcal.mol-1 within the temperature range of 10 degrees-- --70 degrees).

Bacterial Chromatophores↗

PubMed1975

Resolution and reconstitution of Rhodospirillum rubrum pyridine dinucleotide transhydrogenase. Proteolytic and thermal inactivation of the membrane component.

Pyridine dinucleotide transhydrogenase of the Rhodospirillum rubrum chromatophore membrane was readily resolved by a washing procedure into two inactive components, a soluble transhydrogenase factor protein and an insoluble membrane-bound factor. Transhydrogenation was reconstituted on reassociation of these components. The capacity of the membrane factor to reconstitute enzymatic activity was lost after proteolysis of soluble transhydrogenase factor-depleted membranes with trypsin. NADP+ or NADPH, but neither NAD+ nor NADH, stimulated by several fold the rate of trypsin-dependent inactivation of the membrane factor. Substantial protection of the membrane factor from proteolytic inactivation was observed in the presence of Mg2+ ions, an inhibitor of transhydrogenation, or when the soluble transhydrogenase factor was bound to the membrane. Coincident with the loss of enzymatic reconstitutive capacity of the membrane factor was a loss in the ability of the membranes to bind the soluble transhydrogenase factor in a stable complex. The membrane component was inactivated by preincubating soluble transhydrogenase factor-depleted membranes at temperatures above 45 degrees. NADP+, NADPH, or Mg2+ ions, but neither NAD+ nor NADH, protected against inactivation. These studies indicate that (a) the binding of NADP+ or NADPH to the membrane factor promotes a conformational alteration in the protein such that its themostability and susceptibility to proteolysis are increased, and (b) the inhibitory Mg2+ ion-binding site resides in the membrane component.

Bacterial Chromatophores↗

PubMed1978

[Subcellular distribution and several properties of the cAMP enzyme system of phototrophic bacteria].

In the cells of the phototrophic bacteria Rhodospirillum rubrum and Rhodopseudomonas palustris the two enzymes of the cAMP system enzymes - adenylate cyclase and cAMP phosphodiesterase (PDE) exist in a soluble and membrane-bound forms. After mild disruption of the cells (sonication up to 3 min) the activity of both enzymes is found in the chromatophores. In the cells of the two types of bacteria grown under anaerobic conditions soluble adenylate cyclase is predominant. In the cells of R. rubrum the soluble form of PDE posesses higher activity, whereas in the cells of Rh. palustris a higher activity is observed in the membrane-bound form. In addition to their different localization in the cells, the PDE forms of Rh. rubrum differ in their ratios to the concentrations of hydrogen ions and bivalent metals; the latter difference, however, may be accounted for by the effect of a protein modulator of PDE. The pH optimum of membrane-bound PDE is 9.15. Soluble PDE has two activity maxima at pH 7.5 and 8.7. It is probable that similar to the animal tissue enzyme, PDE from Rh. rubrum exists in the soluble phase in at least tw forms. Close pH optima for soluble adenylate cyclase and for one of the soluble PDE forms (about 8.5) may indicate the unidirectional control of these enzymes by hydrogen ion concentration.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMedDate not supplied

[Kinetic model of the effect of dehydration on electron transfer from membrane-bound cytochrome c to the photosynthetic reaction center].

Amplitude characteristics and kinetics of laser-induced oxidation of high-potential cytochrome CH by a photosynthetic reaction center (RC) were investigated in Ectothiorhodospira shaposhnikovii chromatophore preparations of various humidity. It is shown that the diminuition of the amount of oxidized cytochrome and the decrease of the rate of the reaction on lowering the preparation humidity can be explained in terms of the concept of conformation-controlled electron transfer within the CH-RC complex. A model is suggested which predicts that the reversible transition of the complex from one conformational state which allows electron transfer ("contact" state) to the other in which the transfer is impossible ("non-contact" state) is the result of drying (or low temperature) induced changes in the electron tunnelling path in the region of "contact" of the cytochrome CH and RC protein globules.

Bacteria↗

PubMed1978

Electric field-induced polarization of photosynthetic membranes and reaction centers of Rhodopseudomonas sphaeroides, strain 1760-1.

Electric fields of 10(5) V/cm cause the polarization of chromatophore and reaction center films prepared from photosynthesizing purple bacteria. Photosynthetic pigments, and in particular carotenoids, the absorption spectra of which are changed in response to electric fields (electrochromism), may serve as intrinsic indicators of the development of a polarized state. Polarization occurs due to changes in the orientation and the spatial position of different charged groups and particles. The field-induced polarized state can be fixed by exposure to low temperature (-120 degrees C). On being heated, the system relaxes to the initial state and this can be seen as a thermodepolarization current in an electric circuit. The effects of hydration, chemical modification or heat treatment on thermodepolarization current indicate the involvement of macromolecular components in the formation of a polarized state. In light-adapted samples the polarization effect is markedly greater, indicating that conformational changes occur during the primary photoact. It is assumed that the polarization of the reaction centers during electron transfer might be involved in the stabilization of separated charges and in the storage of energy.

Bacterial Chromatophores↗

PubMedDate not supplied

[Polarization of photosynthetic membranes and reaction centers of Rhodopseudomonas sphaeroides 1760-1 in an external electrical field].

Electric fields as high as 10(5) V/cm cause polarization of chromatophores and reaction centre films prepared from photosynthesizing bacteria. Photosynthetic pigments, carotenoids in particular, the absorption spectra of which are changed in response to electric fields, may serve as an intrinsic indicator of the development of a polarized state. Polarization occurs due to changes in orientation and spacial position of different charge groups and particles. The field-induced polarized state can be fixed up by exposure to low temperature (-120 degrees C). While heating the system relaxes to the initial state and this can be seen as a current in an electric circuit. The effects of hydration, chemical modification or heat treatment on current indicate the involvement of macromolecule components in the formation of a polarized state, In light-adapted samples the polarization effect is markedly greater and this can indicate that conformational changes occur during the primary photoact. It is supposed that polarization might be implicated in the stabilization of separated charges and in the storage of energy.

Bacterial Chromatophores↗

PubMed1985

Influence of light on long-term ADP phosphorylation.

ADP phosphorylation coupled to cyclic electron transport was studied over a long period using immobilized chromatophores from Rhodopseudomonas capsulata. Photophosphorylation of ADP as a function of time was continuously measured under different conditions of continuous illumination and concentration of oxygen. Using a red cutoff filter, it was possible to sustain ADP phosphorylation at a maximal rate for more than 10 days, whereas inactivation had always been observed after 5 days when white light was used. The influence of light nature on inactivation was demonstrated using photopigment absorption spectra.

Adenosine Diphosphate↗

PubMedDate not supplied

[Effect of dehydration on the primary picosecond stages of charge separation in Rhodospirillum rubrum].

Effects of dehydration on the quantum yield of charge separation in the reaction centres, fluorescence and nanosecond recombination luminescence in R. rubrum chromatophores have been investigated. It has been shown that dehydration results in more than a 10 times decrease in the quantum efficiency of photosynthesis. Besides, photoinduced fluorescence changes practically disappear in dehydrated samples and the parameters of nanosecond luminescence substantially change. These observations indicate that strong dehydration causes a deterioration of the primary charge separation process at the early picosecond stages of excitation energy transduction into energy of separated charges. This is, probably, due to either changes in the dynamic characteristics of the reaction centre pigment-protein complex or alteration in the structure state (spacings and mutual orientations) of the primary reactants involved in the primary charge separation.

Bacterial Chromatophores↗

PubMed1980

[Structural organization of membranes reconstituted from phospholipids and subchromatophore pigment-protein complexes].

Pigment--protein complexes of the P870 reaction centers and complexes of the bacteriochlorophyll light-harvesting antenna were isolated from the chromatophores of the non-sulfur purple bacterium Rhodospirillum rubrum by solubilization with detergents. The proteoliposomes containing the reaction centers or reaction centers and the light-harvesting antenna as well as liposomes formed from phospholipids were obtained by a self-assembly procedure using seya bean phospholipids. The freeze-fracture study showed that the proteoliposomes contain a large amount of globular particles. The particles incorporated into the two types of the proteoliposomes were distinguished in size. The globules of the reaction center and antenna complexes were bigger in size than the reaction center globules. The globular structures were not found in the liposomal membranes. The liposomes formed in the absence of the pigment--protein complexes were predominantly the multilamellar vesicles. The proteoliposomes were mostly represented as monolamellar membrane vesicles. The spatial arrangement of the reaction center complexes in the membranes is discussed.

Bacterial Chromatophores↗

PubMedDate not supplied

[Study of chromophore dynamics by means of Rayleigh scattering of Mossbauer radiation].

The temperature dependence of rayleigh scattering of Mössbauer radiation was studied for two samples of the chromatophores with different relative humidity (P/Ps = 0.35 and 0.94). New type of motion--the transitions between conformational substates was found above 200 degrees K. The model was developed to describe conformational motion in the membranes and membrane proteins. A new formula was derived for the Debye--Waller factor in accordance with this model. The model proposes the existence of fluid-like motions of protein fragments within the volume of some A3, restricted by the profile of the conformational potential. The correlation between decreasing of fR and increasing of electron transition rate was observed.

Bacterial Chromatophores↗

PubMedDate not supplied

[Effect of deuteration on the kinetics of photoinduced electron transport in the reaction centers of purple bacteria].

Substitution of H2O for D2O in the preparations of reaction centres from chromatophore membranes of photosynthesizing bacteria Rhodopseudomonas sphaeroides, 1760-1 results in a decrease of the efficiency of direct electron transfer from photoreduced primary quinone X1- to the secondary ones and in rising possibilities for reversible reaction X1- with photooxidized bacteriochlorophyll. The value of isotope effect which does not usually exceed 1.2 depends on temperature; it is not found in the temperature range below -60 degrees divided by -80 degrees C.

Bacterial Chromatophores↗

PubMed1976

Reconstitution of biological molecular generators of electric current. Bacteriochlorophyll and plant chlorophyll complexes.

1. Electric generation by bacteriochlorophyll reaction center complexes from Rhodospirillum rubrum and by photosystem I complexes from pea chloroplasts has been studied. 2. The methods for the proteoliposome reconstitution from azolectin and bacteriochlorophyll- or plant chlorophyll-containing protein complexes have been elaborated. Light-dependent electric responses of the proteoliposomes were detected using (a) phenyldicarbaundecarborane anion (PCB-) probe and (b) direct measurement by a voltmeter in the proteoliposome-planar phospholipid membrane system. 3. Both PCB- and direct measurements demonstrated that bacteriochlorophyll proteoliposomes are competent in light-dependent electric generation (plus outside proteoliposomes). The photoelectric effect was shown to increase on addition of tetramethyl-p-phenylenediamine (TMPD), CoQ6, and vitamin K3, and to decrease on addition of ferricyanide, o-phenanthroline and a protonophorous uncoupler. Estimation of the photoelectromotive force of the bacteriochlorophyll proteoliposome-planar membrane system gave a value of about 0.2 V. The action spectrum of the photoelectric effect was similar to the absorption spectrum of the bacteriochlorophyll complex. 4. Reconstitution of proteoliposomes containing bacteriochlorophyll centers and bacteriorhodopsin resulted in the system generating an electric field whose direction can be changed by varying the spectral composition of the light: the red light, exciting bacteriochlorophyll, induces negative, and the green light, exciting bacteriorhodopsin, induces positive charging of the proteoliposome interior. 5. Association of isolated R. rubrum chromatophores with planar phospholipid membrane was found to give a system demonstrating light-induced electric generation as high as 215 mV in the presence of napthoquinone, TMPD (or phenazine methosulfate, PMS), and ascorbate. Under the same conditions, addition of inorganic pyrophosphate or ATP results in formation of an electric field of the same direction as that induced by light. 6. Proteoliposomes with plant chlorophyll complexes of photosystem I demonstrated light-induced PCB- responses indicating formation of the electric field with plus inside vesicles. The effect required PMS addition. A protonophorous uncoupler and o-phenanthroline were inhibitory. Electric responses in the chlorophyll proteoliposome-planar membrane system were very small (not higher than 10 mV).

Bacterial Chromatophores↗

PubMedDate not supplied

[Potential difference across the membrane of subcellular particles. II. Proton channels in oxidative photophosphorylation].

A photo-electrochemical hypothesis of cyclic photophosphorylation in chromatophores suggests that electrons, thrown out by light from the reaction center, came back via the electron carrier chain within the hydrophobic part of the membrane taking up H+-ions through the entrance H+-channels. H+-ions and electrons are transferred to quinones or semiquinones which are transformed into semiquinones or hydroquinones accordingly. They release H+-ions into output channels, while the electrons are transferred to the next electron carrier. At non-cyclic photophosphorylation of the chloroplast the second photosystem takes electrons from water via primary donor and releases the H+-ions into the proton channels. After receiving an electron the oxidase takes up H+ through the H+-channels and gives the electron and H+ to O2. A direct method of the experimental check up of the electrochemical hypothesis is described.

Biological Transport, Active↗