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PubMed1979

Transport of local anaesthetics across chromatophore membranes.

1. Both simple amines and tertiary amino local anaesthetics give rise to an accelerated decay of the absorption change of added pH indicator dyes and a decelerated decay of the endogenous carotenoid absorption band shift, following short flash excitation of Rhodopseudomonas sphaeroides chromatophores. 2. With increasing medium pH, lower concentrations of amine or local anaesthetics are effective. 3. The order of potency of the local anaesthetics concurs with their reported membrane/buffer partition coefficients and concentrations required for action potential blockade in nerve fibres. 4. The data are taken as evidence for rapid transport of the free base across the chromatophore membrane and relatively slow penetration of the protonated local anaesthetic. Protolytic reactions complete the effective dissipation of the trans-membrane pH gradient. 5. Benzocaine, with its unusually low pKa and the quaternary derivative, chloropromazine methiodide do not display this type of behaviour. 6. In the presence of membrane potential-collapsing agents, such as valinomycin/K+ or thiocyanate ions, local anaesthetics decelerate the decay of the cresol red change but have no effect on the carotenoid shift decay. It appears that transport of the unprotonated local anaesthetic although electrically neutral, requires the presence of a membrane potential. 7. In contrast, the non-anaesthetic amines act independently of the membrane potential. 8. Ca2+ interferes with the mechanism of local anaesthetic deceleration of the cresol red change decay in the presence of valinomycin/K+ or thiocyanate but not with other anaesthetic or amine reactions.

Bacterial Chromatophores↗

PubMed1979

The resonance Raman spectrum of carotenoids as an intrinsic probe for membrane potential. Oscillatory changes in the spectrum of neurosporene in the chromatophores of Rhodopseudomonas sphaeroides.

The resonance Raman spectrum of the carotenoid neurosporene is shown to be a sensitive monitor of absorption shifts, and thus changes in membrane potential, in chromatophores of the GlC mutant of Rhodopseudomonas sphaeroides. For a Raman excitation wavelength at 472.7 nm, the intensities of the two most prominent resonance Raman features (v1 and v2) respond very differently to small shifts in the absorption maxima. Thus, the ratio intensity v1/intensity v2 is a sensitive probe for absorption shifts. Changes in this ratio of approximately 20% were observed during a valinomycin induced diffusion potential. At 5 degrees C changes in the average intensity ratio of +6, -4 and -14% were brought about by oligomycin, FCCP and sodium deoxycholate, respectively. The changes in intensity ratio were temperature dependent and, in addition, effects due to the laser beam acting as an actinic light could be detected. Oscillatory changes were observed in absolute Raman and Rayleigh scattering intensities for chromatophores at 5 degrees C and for intact cells under growing conditions.

Bacterial Chromatophores↗

PubMed1980

Photo-induced electron transport and water state in Rhodospirillum rubrum chromatophores.

It is shown that in bacterial chromatophores the pronounced changes in the free water content with a proton spin-spin relaxation time (T2) of 10(-3)--10(-2) s does not influence the efficiency of electron transfer from the photosynthetic reaction centre to the membrane pool of secondary acceptors. An abrupt inhibition of this process occurs only after the loss of the water with faster proton spin-spin relaxation time (T2 of 10(-4) s). The process is reversible. The water fraction in question is obviously bound to the chromatophore proteins and forms the primary hydration layer.

Bacterial Chromatophores↗

PubMed1995

Characterization of 9-aminoacridine interaction with chromatophore membranes and modelling of the probe response to artificially induced transmembrane delta pH values.

We analyze the adsorption of the fluorescent monoamine 9-aminoacridine to the membrane phase of photosynthetic chromatophores, in the physiological interval of pH values ranging from 5.5 to 8.5 and at ionic strengths of 0.005 and 0.150 M. The interaction of the probe with the membrane phase is described with S-shaped isotherms of the Hill type and is modulated by electrostatic effects as modelled with the Gouy-Chapman-Boltzman theory. This description is consistent with different values of the surface change density of the chromatophore membranes decreasing from about 1.3 x 10(-3) to about 0.5 x 10(-3) e-/A2, on changing the pH from 8.5/7.5 to 6.5/5.5, respectively. Furthermore we show that, when the free concentrations of the probe in the inner and outer vesicle compartments are computed from the adsorbing isotherms at the proper pH values, the model considering the equilibrium distribution of the neutral monoamine following the onset of a delta pH is sufficient to describe the dependence of the artificially induced transmembrane delta pH values on the observed quenching of the probe fluorescence.

Aminacrine↗

PubMed1994

Flash-induced electrogenic reactions in the SA(L223) reaction center mutant in Rhodobacter sphaeroides chromatophores.

The charge transfer events in the SA(L223) reaction center mutant Rhodobacter sphaeroides chromatophores were investigated by direct electrometry. Besides the primary charge separation, the small stigmatellin-sensitive electrogenic reaction due to the electron transfer from the primary to the secondary quinone acceptor in the reaction center complex was observed after the first flash. The second flash-induced electrogenic phase of the secondary quinone protonation and subsequent electrogenic reactions of the cytochrome bc1 complex were much slower than those in chromatophores of the wild type. It is suggested that replacement of Ser-L223 by Ala impairs both specific proton-conducting pathways leading to the secondary quinone QB.

Alanine↗

PubMed1985

Evidence for L-glutamate as a transmitter substance of motoneurons innervating squid chromatophore muscles.

Motor nerve branches were stimulated in the dermis layer prepared from isolated pieces of dorsal mantle skin of the squid Lolliguncula brevis and the contractions of chromatophore muscle fibers were recorded with the aid of a photo-electric transducer. L-Glutamate (L-Glu), kainate and quisqualate caused a contracture and often repetitive twitch-like contractions. These effects were readily reversible. In the case of L-Glu application, twitches induced by single stimuli applied to motor nerves were enhanced and prolonged. The glutamate antagonists glutamic acid gamma-methyl ester, glutamic acid diethyl ester, D,L-2-amino-4-phosphonobutyrate and gamma-D-glutamylglycine prevented both nerve induced and L-Glu induced contractions. The NMDA-receptor agonists N-methyl-D-aspartate, L-aspartate and D-glutamate, and their antagonists alpha-aminoadipate and D,L-2-amino-5-phosphonovalerate were found ineffective. With the aid of saline media of different Ca and Mg content, it was possible to selectively eliminate one or all components of the effect of L-Glu. Tetrodotoxin abolished nerve induced contractile responses but did not interfere with the contracture caused by L-Glu. Intracellular electrical recording indicated that nerve stimulation causes EPSPs which do not give rise to spike discharges. The results are compatible with the hypothesis that L-Glu is a transmitter substance of the motoneurons that innervate chromatophore muscle fibers.

Animals↗

PubMed1972

The photoreduction of nicotinamide-adenine dinucleotide by chromatophore fractions from Rhodospirillum rubrum.

The photoreduction of nicotinamide-adenine dinucleotide (NAD(+)), catalyzed by chromatophore fractions from young (1 day) and old (4-5 days) cultures of Rhodospirillum rubrum, was measured in the presence of either succinate or 2,6-dichlorophenol indophenol (DPIP) and an excess of ascorbate. The time-course of photoreduction in the succinate system suggested a "reversed electron flow" from the donor to NAD(+) mediated by a high energy intermediate produced by a light-induced, cyclic electron transport in the chromatophore fractions. The effects of the uncoupler carbonyl cyanide [p-(trifluoromethoxy)phenyl]hydrazone (FCCP) and of the inhibitors antimycin A and 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO) were consistent with this interpretation. The time-course of NAD(+) photoreduction in the presence of DPIP and ascorbate suggested a direct, light-induced electron transport from the donor to the acceptor. We cannot yet distinguish between a model in which the same reaction center is utilized in the photoreduction by both donor systems (the reaction center component P-870 may relate to two primary acceptors at different redox potential levels) and a model in which each photoreducing system is driven by its own reaction center component.

Antimycin A↗

PubMed2000

Fusion of chromatophores from photosynthetic bacteria with a supported lipid layer: characterization of the electric units.

Direct electrometric measurements of membrane potential changes are a valuable tool for study of vectorial transfer of electrons, protons, and ions. Commonly model membrane systems are created by fusion of lipid/protein vesicles with lipid-coated thin films. We characterized the electric units resulting from this process using chromatophores from the purple bacterium Rhodobacter sphaeroides and either a Mylar film or a planar modified gold electrode as support. Investigation of the shunting activity of the ionophore gramicidin on the flash-induced potential change demonstrates fusion of individual chromatophores to form independent 'blisters', which preserve an interior aqueous compartment. Under current-clamp conditions the photovoltage follows the change of the membrane potential of the individual blisters.

Bacterial Chromatophores↗

PubMed1993

Fourier transform infrared study of the primary electron donor in chromatophores of Rhodobacter sphaeroides with reaction centers genetically modified at residues M160 and L131.

Structural changes in chromatophores of Rhodobacter sphaeroides reaction center mutants associated with the substitution of amino acid residues near the primary electron donor P have been investigated by light-induced FTIR difference spectroscopy. The single-site mutations Leu-L131 to His and Leu-M160 to His and the corresponding double mutation were designed to introduce a proton-donating residue that could form a hydrogen bond with the keto carbonyl of ring V of each bacteriochlorophyll (PL and PM) of the dimer. The presence of large positive bands at approximately 1550, 1480, and 1295 cm-1, as well as at 2600-2800 cm-1 in the light-induced P+QA-/PQA FTIR difference spectra, corresponding to the photooxidation of P and the photoreduction of the primary quinone QA, demonstrates that the BChl dimer state of P+ is preserved in the LH(L131), LH(M160), and LH(M160)+LH(L131) mutants, although frequency shifts and amplitude changes can be observed, notably for LH(M160). Compared to wild type, these changes are thought to reflect a different charge repartition over the two BChls in P+. Large frequency downshifts in the 9-keto C=O stretching region of the P+QA-/PQA FTIR difference spectra of chromatophores are observed in the mutant samples relative to wild type. For the LH(M160) mutant, a large differential signal at 1678/1664 cm-1 is assigned to a shift, upon photooxidation, of the 9-keto C=O of PM hydrogen-bonded to His-M160, while that at 1718/1696 cm-1 corresponds to the free 9-keto C=O of PL.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial Chromatophores↗

PubMed1990

P+QA- and P+QB- charge recombinations in Rhodopseudomonas viridis chromatophores and in reaction centers reconstituted in phosphatidylcholine liposomes. Existence of two conformational states of the reaction centers and effects of pH and o-phenanthroline.

The P+QA- and P+QB- charge recombination decay kinetics were studied in reaction centers from Rhodopseudomonas viridis reconstituted in phosphatidylcholine bilayer vesicles (proteoliposomes) and in chromatophores. P represents the primary electron donor, a dimer of bacteriochlorophyll; QA and QB are the primary and secondary stable quinone electron acceptors, respectively. In agreement with recent findings for reaction centers isolated in detergent [Sebban, P., & Wraight, C.A. (1989) Biochim. Biophys. Acta 974, 54-65] the P+QA- decay kinetics were biphasic (kfast and kslow). Arrhenius plots of the kinetics were linear, in agreement with the hypothesis of a thermally activated process (probably via P+I-; I is the first electron acceptor, a bacteriopheophytin) for the P+QA- charge recombination. Similar activation free energies (delta G) for this process were found in chromatophores and in proteoliposomes. Significant pH dependences of kfast and kslow were observed in chromtophores and in proteoliposomes. In the pH range 5.5-11, the pH titration curves of kfast and kslow were interpreted in terms of the existence of three protonable groups, situated between I- and QA-, which modulate the free energy difference between P+I- and P+QA-. In proteoliposomes, a marked effect of o-phenanthroline was observed on two of the three pKs, shifting one of them by more than 2 pH units. On the basis of recent structural data, we suggest a possible interpretation for this effect, which is much smaller in Rhodobacter sphaeroides. The decay kinetics of P+QB- were also biphasic. Marked pH dependences of the rate constants and of the relative proportions of both phases were also detected for these decays. The major conclusion of this work comes from the biphasicity of the P+QB- decay kinetics. We had suggested previously that biphasicity of the P+QA- charge recombination in Rps. viridis comes from nonequilibrium between protonation states of the reaction centers due to comparable rates of the protonation events and charge recombination. This hypothesis does not hold since the P+QB- decays occur on a time scale (tau approximately 300 ms at pH 8) much longer than protonation events. This leads to the conclusion that kfast and kslow (for both P+QA- and P+QB-) are related to conformational states of the reaction centers, existing before the flash. In addition, the fast and slow decays of P+QB- are related to those measured for P+QA-, via the calculations of the QA-QB in equilibrium QAQB- apparent equilibrium constants, K2.(ABSTRACT TRUNCATED AT 400 WORDS)

Bacterial Chromatophores↗

PubMed2001

The yellow mutation in the frog Rana rugosa: pigment organelle deformities in the three types of chromatophore.

Crossing experiments revealed that a single recessive gene mutation (yellow) gives rise to the yellow phenotype of Rana rugosa in Japan. Ultrastructural observation of dermal chromatophores showed that the pigment organelles; melanosomes, pterinosomes, and reflecting platelets, all had structural deformities. This suggests that the yellow gene acts at the level of a primordial pigment organelle common to the three types of chromatophore.

Animals↗

PubMed1974

The detection and characterization by electron-paramagnetic-resonance spectroscopy of iron-sulphur proteins and other electron-transport components in chromatophores from the purple bacterium Chromatium.

Low-temperature e.p.r. (electron-paramagnetic-resonance) spectroscopy was used to detect electron-transport components in Chromatium chromatophores with e.p.r. signals in the g=2.00 region. High-potential iron protein (E(m8.0)=+325mV, where E(m8.0) is the midpoint potential at pH8) and a second component (g=1.90, E(m8.0)=+285mV) are oxidized in illuminated chromatophores. Two iron-sulphur proteins (g=1.94) with E(m8.0)=-290mV and E(m8.0)=-50mV are present. One (E(m8.0)=-50mV) is reduced on illumination. A component (g=1.82) with E(m8.0)=-135mV is photoreduced at 10 degrees K. The midpoint potential of this component is altered by o-phenanthroline and pH. The properties of this component suggest that it is the primary electron acceptor of a photochemical system. Another component (g=1.98) also has some of the properties of a primary electron acceptor, but its function cannot be completely defined. These results show that iron-sulphur proteins are present in the electron-transport system of Chromatium and indicate their role in electron transport.

Bacterial Chromatophores↗

PubMed1978

Isolation of a membrane protein from R rubrum chromatophores and its abnormal behavior in SDS-polyacrylamide gel electrophoresis due to a high binding capacity for SDS.

A membrane protein insoluble in water was isolated by gel chromatography in the presence of 0.1% sodium dodecyl sulfate (SDS) from chromatophores of a photosynthetic bacterium, Rhodospirillum rubrum. This is one of the major membrane proteins of the chromatophore. The protein was found to bind about four grams of SDS per gram, a value which is more than twice the amount generally observed with protein polypeptides derived from water-soluble globular proteins. The electrophoretic behavior of the complex between the membrane protein and SDS is abnormal due to this high capacity for binding SDS. Estimation of the molecular weight of this protein by SDS-polyacrylamide gel electrophoresis was thus impossible. Such an anomaly in SDS binding is unlikely to be restricted to the particular membrane protein described in this paper. The possibility of such a deviation from standard behavior in the interaction with SDS should be taken into consideration in studies of other membrane proteins, since SDS is often used both in analytical and preparative procedures.

Bacterial Chromatophores↗

PubMed1978

Diffusion-potential-induced oxidation and reduction of cytochromes in chromatophores from Rhodopseudomonas sphaeroides.

A membrane potential jump was induced by the addition of valinomycin in the presence of a KCl concentration gradient across the membrane of Rhodopseudomonas sphaeroides chromatophores. As well as a carotenoid band shift, which is known to be an indicator of membrane potential, absorbance changes due to the oxidation-reduction reactions of cytochromes accompanied the jump. Under aerobic conditions with no reductant added, a part of cytochrome c2 was reduced by an inside-positive potential jump of about 100 mV in the time range of tens of seconds. This can be explained by the location of the cytochrome on the inner side of the chromatophore membrane and electrophoretic flow of electrons across the membrane. On the other hand, in the presence of 1 mM ascorbate, a similar jump of membrane potential induced a rapid oxidation of cytochrome c2 and a subsequent reduction. A rapid reduction of b-type cytochrome was also observed. Antimycin A inhibited the c2 oxidation, but did not inhibit the b reduction. The oxidation of cytochrome c2 may be explained by a diffusion-potential-induced electron flow to cytochrome b and a simultaneous electron donation by cytochrome b and cytochrome c2 to a common electron acceptor, possibly a quinone.

Anaerobiosis↗

PubMed1980

Effects of surface potential on the equilibrium and kinetics of redox reactions of membrane components with external reagents in chromatophores from Rhodopseudomonas sphaeroides.

The characteristics of the salt and pH dependences of the redox levels of cytochrome c2 and reaction center bacteriochlorophyll were studied in chromatophores from Rhodopseudomonas sphaeroides. They could be explained in terms of the difference of redox potential in the membrane from that in the bulk aqueous phase due to the electrostatic potential difference arising from charges fixed on the membrane surface. The midpoint potentials (Em) became lower when the surface potential (the electrostatic potential at the surface with reference to the bulk aqueous phase) had large negative values at lower salt concentrations at neutral pH, as predicted by the Gouy-Chapman theory. The rate of oxidation of cytochrome c2 in chromatophores by ferricyanide also depended on salt and pH levels. The rate was low at low salt concentrations, probably because of the lower surface concentration of ferricyanide compared with the bulk concentration, due to the surface potential.

Bacterial Chromatophores↗

PubMed1976

The control of the adenosine triphosphatase of Rhodospirillum rubrum chromatophores by divalent cations and the membrane high energy state.

1. The rate of ATP hydrolysis, catalysed by Rhodospirilum rubrum chromatophores is accelerated by low concentrations and inhibited by high concentrations of uncoupling agent. 2. The inhibition at high concentrations of uncoupling agent is potentiated by the presence of free magnesium ions. At low uncoupler concentrations magnesium has no effect on the rate of ATP hydrolysis. 3. Inhibition of ATP hydrolysis by high concentrations of uncoupling agent and free magnesium ions is reversed by illumination. Illumination has less effect at low magnesium concentrations. 4. Free calcium ions inhibit ATP hydrolysis independently of the coupled state of the membrane. 5. Under coupled conditions, magnesium ions can overcome the inhibition induced by calcium. The two ions complete for the same site on the enzyme. 6. Inhibition by free magnesium in highly uncoupled chromatophores and inhibition by free calcium are both non-competitive with respect to the divalent cation-ATP substrate. 7. These data are consistent with a model in which divalent cations can bind to a site on the enzyme which is distinct from the substrate site. The regulation of the enzyme activity by the high energy state of the membrane is dependent on the occupant of this site.

Adenosine Triphosphatases↗

PubMed1977

The effect of electron donors and acceptors on light-induced absorbance changes and photophosphorylation in Rhodospirillum rubrum chromatophores.

Light-induced difference spectra between 400 and 640 nm of Rhodospirillum rubrum chromatophores were performed in the presence and absence of exogenous electron donor/acceptor systems and compared with the chemical oxidation spectrum. The results indicate that the component previously defined as P430 is not a unique entity but rather represents different species, or a mixture of species, under various conditions. Under all conditions in which the reaction center bacteriochlorophyll is reversibly photooxidized, as indicated by the bleaching around 600 nm, it is also contributing to the absorbance increase around 430 nm. In one case, in presence of reduced dichloroindophenol and in the absence of oxygen, the photooxidation of reaction center bacteriochlorophyll is fully supressed. Under these conditions an irreversible change around 430 nm is still observed and seems to be due to the Soret band of b-type cytochrome. In the presence of reduced dichloroindophenol and absence of oxygen there is a marked inhibition of photophosphorylation. This inhibition is apparently due to the complete reduction of the cyclic electron carriers. Addition of the low potential dye benzyl viologen facilitates an almost complete recovery of the reversible photooxidation of reaction center bacteriochlorophyll as well as of photophosphorylation. These results indicate that the apparent mid-point potential of the primary electron acceptor in Rhodospirillum rubrum chromatophores is probably in the range of that of benzyl viologen (E'o = - 340 mV).

2,6-Dichloroindophenol↗

PubMed1982

Photooxidase system of Rhodospirillum rubrum III. The role of rhodoquinone and ubiquinone in the activity of preparations of chromatophores and photoreaction centers.

The role of rhodoquinone and ubiquinone in the oxygen photoreducing (photooxidase) activity of Rhodospirillum rubrum was investigated. The sole addition of purified rhodoquinone restored photooxidase activity in isolated chromatophores which had been extracted with organic solvents and which were apparently free of secondary acceptor ubiquinone. Rhodoquinone also enhanced photooxidase activity in photoreaction center preparations from which secondary ubiquinone seemed to have been removed. Those results suggest that rhodoquinone accepts electrons directly from primary ubiquinone during chromatophore photooxidase activity. In contrast, rhodoquinone does not participate in the basal activity of photoreaction center preparations, which seems to result from the autooxidation of both primary and secondary ubiquinone.

Bacterial Chromatophores↗