Photooxidase activity of Rhodospirillum rubrum chromatophores and reaction center complexes. The role of non-cyclic electron transfer in generation of the membrane potential

The mechanism of light-induced O₂ uptake by chromatophores and isolated P-870 reaction center complexes from Rhodospirillum rubrum has been investigated.The process is inhibited by o-phenanthroline and also by an extraction of loosely bound quinones from chromatophores. Vitamin K-3 restored the o-phenanthroline-sensitive light-induced O₂ uptake by the extracted chromatophores and stimulated the O₂ uptake by the reaction center complexes. It is believed that photooxidase activity of native chromatophores is due to an interaction of loosely bound photoreduced ubiquinone with O₂. Another component distinguishable from the loosely bound ubiquinone is also oxidized by O₂ upon the addition of detergents (lauryldimethylamine oxide or Triton X-100) to the illuminated reaction center complexes and to the extracted or native chromatophores treated by o-phenanthroline. Two types of photooxidase activity are distinguished by their dependence on pH.The oxidation of chromatophore redox chain components due to photooxidase activity as well as the over-reduction of these components in chromatophores, incubated with 2,3,5,6-tetramethyl-p-phenylenediamine (Me₄Ph(NH₂)₂) or N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD) (plus ascorbate) in the absence of exogenous electron acceptors, leads to an inhibition of the membrane potential generation, as measured by the light-induced uptake of penetrating phenyldicarbaundecaborane anions (PCB^?) and tetraphenylborate anions. The inhibition of the penetrating anion responses observed under reducing conditions is removed by oxygen, 1,4-naphthoquinone, fumarate, vitamin K-3 and methylviologen, but not by NAD⁺ or benzylviologen. Since methylviologen does not act as an electron acceptor with the extracted chromatophores, it is believed that this compound, together with fumarate and O₂, gains electrons at the level of the loosely bound ubiquinone. Data on the relationship between photooxidase activity and membrane potential generation by the chromatophores show that non-cyclic electron transfer from reduced Me₄Ph(NH₂)₂ to the exogenous acceptors is an electrogenic process, whereas non-cyclic electron transfer from reduced TMPD is non-electrogenic.Being oxidized, Me₄Ph(NH₂)₂ and TMPD are capable of the shunting of the cyclic redox chain of the chromatophores. Experiments with extracted chromatophores show that the mechanisms of the shunting by Me₄Ph(NH₂)₂ and TMPD are different.     

Photooxidase activity of isolated chromatophores and intact cells of phototrophic bacteria

Illumination causes an uptake of oxygen by isolated chromatophores of purple and green bacteria incubated with electron donors. Photooxidase activity of Rhodospirillum rubrum, Chromatium minutissimum, Rhodopseudomonas sphaeroides and Thiocapsa roseopersicina chromatophores is sensitive, and photooxidase activity of Ectothiorhodospira shaposhnikovii and Chlorobium limicola f. thiosulfatophilum is resistant to o-phenanthroline. O₂ uptake by illuminated chromatophores of R. rubrum and C. limicola is stimulated upon the increase of pH of incubation mixture from 5 to 9. Photooxidase activity is also manifested in the intact bacterial cells and not merely in the isolated chromatophores. O₂ uptake by the illuminated R. rubrum cells treated with CN^- is stimulated by 2-heptyl-4-hydroxyquinoline-N-oxide and a protonophorous uncoupler. The interaction of the photosynthetic and respiratory systems of the electron transfer in the bacterial cells and the probable causes of the strong anaerobic way of life of the green sulfur bacteria are discussed.HQNO 2-heptyl-4-hydroxyquinoline-N-oxide - TMPD N,N,-N,N-tetramethyl-p-phenylenediamine     

Reversible effect of intensive light on photobiochemical properties of Rhodospirillum rubrum chromatophores

The effect of high intensity (photosynthesis-saturating) light on the optical properties of the bacteriochlorophyll and the light-induced H+ uptake by R. rubrum chromatophores was studied. It was shown that under aerobic conditions illumination causes reversible inhibition (in the dark) of the chromatophore ability for the light-induced uptake of H+, a reversible inhibition of the photosynthetical reaction center function and irreversible bleaching of the antennal bacteriochlorophyll. A kinetic comparison of spectral effects and reversible changes in pH as well as the effects of atmospheric oxygen and exogenous electron donors suggests that inhibition of photoactivity of the chromatophores upon illumination is due to accumulation of oxidized bacteriochlorophyll in the reaction center.     

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.     

Time-resolved infrared studies of light-induced processes in plant thylakoids and bacterial chromatophore membranes. Evidence for the function of water molecules and the polypeptides in energy dissipation

Spinach thylakoids and chromatophores from the photosynthetic bacterium Rhodopseudomonas capsulata were investigated by means of time-resolved infrared spectroscopy, using thin water-containing membrane films which fully maintained their photochemical activity. Upon flash excitation, reversible infrared absorbance changes were obtained and their difference spectra were recorded. In spinach thylakoids, these transient signals could be described by a sum of two exponential decay functions with half-times of about 2 and 30 ms, respectively. They were insensitive to the addition of benzyl viologen, ferricyanide or ferricyanide + DCMU. They are ascribed by their dependence on intensity and wavelength range of the actinic flash to processes in the antenna pigment-protein complexes. In chromatophores from photosynthetic bacteria, similar infrared signals in the millisecond time range were obtained. Their spectral distribution was investigated for three mutants of the photosynthetic bacterium and is different for membranes lacking carotenoids. Both signals, in thylakoids and chromatophores, reflect the proportion of absorbed flash energy which is neither channelled to the reaction center nor emitted as light, but is dissipated through radiationless decay. A common feature of the difference spectra from spinach thylakoids and bacterial chromatophores are bands identified by deuteration as being due to H₂O. Some bands are interpreted in terms of water going transiently from the hydrogen-bonded to the free state. Other bands are assigned to the polypeptides of the light-harvesting complexes, and thus indicate their participation in energy dissipation. Membranes from photosynthetic bacteria containing a photochemical reaction center show a distinct slow signal component decaying in about 1 s. It saturates at low flash intensity and is abolished upon chemical oxidation of the primary electron donor. Two bands in the difference spectrum of this component are tentatively assigned to the ester C = O and keto C = O vibrations of photooxidized bacteriochlorophylls in the reaction center. The data suggest that chromophoric and non-chromophoric infrared absorbance changes contribute to the difference spectra, and thus may represent a clue to the processes at the active sites of polypeptides in photosynthesis.     

The Dibromothymoquinone Effect on Membrane Potential Generation in Rhodospirillum rubrum Chromatophores

2,5-Dibromo-3-methyl-6-isopropyl benzoqui-none (DBMIB) inhibits the light-dependent membrane potential generation in Rhodospirillum rubrum chromatophores. The inhibition is relieved by electron donors and is obviously due to oxidation of the photosynthetic electron transfer chain components. In addition, high DBMIB concentrations elicit another effect probably caused by disruption of quinone functions in chromatophores. However, in quinone-depleted chromatophores and proteoliposomes containing the P-870 reaction center and light-harvesting antenna complexes, DBMIB stimulates membrane potential generation in the light, probably restoring some of the quinone-dependent processes in the membrane. DBMIB inhibits the inorganic pyrophosphate- and ATP-in-duced membrane potential generation in chromatophores.     

Blue and red shifts of bacteriochlorophyll absorption band around 880 nm in Rhodospirillum rubrum.

The redox potential dependence of the light-induced absorption changes of bacteriochlorophyll in chromatophores and subchromatophore pigment-protein complexes from Rhodospirillum rubrum has been examined. The highest values of the absorption changes due to the bleaching of P-870 and the blue shift of P-800 in chromatophores and subchromatophore complexes are observed in the 360-410mV redox potential range. At potentials below 300 mV (pH 7.0), the 880 nm band of bacteriochlorophyll shifts to shorter wavelengths in subchromatophore complexes and to longer wavelengths in chromatophores. The data on redox titration show that the red and blue shifts of 880-nm bacteriochlorophyll band represent the action of a non-identified component (C340) which has an oxidation-reduction midpoint potential close to 340 mV (n=1) at pH 6.0--7.6. The Em of this component varies by 60 mV/pH unit between pH 7.6 and 9.2. The results suggest that the red shift is due to the transmembrane, and the blue shift to the local intramembrane electrical field. The generation of both the transmembrane and local electrical fields is apparently governed by redox transitions of the component C340.     

Blue and red shifts of bacteriochlorophyll absorption band around 880 nm in Rhodospirillum rubrum

The redox potential dependence of the light-induced absorption changes of bacteriochlorophyll in chromatophores and subchromatophore pigment-protein complexes from Rhodospirillum rubrum has been examined. The highest values of the absorption changes due to the bleaching of P-870 and the blue shift of P-800 in chromatophores and subchromatophore complexes are observed in the 360–410 mV redox potential range. At potentials below 300 mV (pH 7.0), the 880 nm band of bacteriochlorophyll shifts to shorter wavelengths in subchromatophore complexes and to longer wavelengths in chromatophores.

The data on redox titration show that the red and blue shifts of 880-nm bacteriochlorophyll band represent the action of a non-identified component (C₃₄₀) which has an oxidation-reduction midpoint potential close to 340 mV (n = 1) at pH 6.0–7.6. The E_m of this component varies by 60 mV/pH unit between pH 7.6 and 9.2.

The results suggest that the red shift is due to the transmembrane, and the blue shift to the local intramembrane electrical field. The generation of both the transmembrane and local electrical fields is apparently governed by redox transitions of the component C₃₄₀.     

Light-induced electron transport pathways in membrane preparations from Rhodopseudomonas capsulata

The photosynthetic electron transport chain in Rhodopseudomonas capsulata cells was investigated by studying light-induced noncyclic electron transport from external donors to O₂. Two membrane preparations with opposite membrane polarity, heavy chromatophores and regular chromatophores, were used to characterize this electron transport. It was shown that with lipophylic electron donors such as dichloroindophenol, diaminobenzidine, and phenazine methosulfate the electron transport activities were similar in both types of chromatophores, whereas horse heart cytochrome c, K₄Fe(CN)₆, 3-sulfonic acid phenazine methosulfate, and ascorbate, which cannot penetrate the membrane, were more active in the heavy chromatophores than in the regular chromatophores. Partial depletion of cytochrome c₂ from the heavy chromatophores caused a decrease in the light-induced O₂ uptake from reduced dichloroindophenol or ascorbate. The activity could be restored with higher concentrations of dichloroindophenol or with purified cytochrome c₂ from Rps. capsulata. It is assumed that in the heavy chromatophores the artificial electron donors are oxidized on the cytochrome c₂ level which faces the outside medium. However, cytochrome c₂ is not exposed to the outside medium in the regular chromatophores. Therefore, only lipophylic donors would interact with cytochrome c₂ in this system, while hydrophylic donors would be oxidized by another component of the electron transport chain which is exposed to the external medium. Studies with inhibitors of photophosphorylation show that antimycin A enhances the light-dependent electron transport to O₂ whereas 1:10 phenanthroline inhibited the reaction, but dibromothymoquinone did not affect it. It is assumed that a nonheme iron protein is taking part in this electron transport but not a dibromothymoquinone-sensitive quinone. The terminal oxidase of the light-dependent pathway is different from the two oxidases of the respiratory chain. The ratio between electrons entering the system and molecules of O₂ consumed is 4, which means that the end product of O₂ reduction is H₂O.     

Generation of electric current by chromatophores of Rhodospirillum rubrum and reconstitution of electrogenic function in subchromatophore pigment-protein complexes.

Lipoprotein complexes, containing (1) bacteriochlorophyll reaction centers, (2) bacteriochlorophyll light-harvesting antenna or (3) both reaction centers and antenna, have been isolated from chromatophores of non-sulphur purple bacteria Rhodospirillum rubrum by detergent treatments. The method of reconstituting the proteoliposomes containing these complexes is described. Being associtated with planas azolectin membrane, ptoteoliposomes as well as intact chromatophores were found to generate a light-dependent transmembrane electric potential difference measured by Ag/AgC1 electrodes and voltmeter. The direction of the electric field inproteoliposomes can be regulated by the addition of antenna complexes to the reconstitution mixture. The reaction center complex proteoliposomes generate an electric field of a direction opposite to that in chromatophores, whereas proteoliposomes containing reaction center complexes and a sufficient amount of antenna complexes produce a potential difference as in chromatophores. ATP and inorganic pyrophosphate, besides light, were shown to be usable as energy sources for electric generation in chromatophores associated with planar membrane.     

Functional consequences of the organization of the photosynthetic apparatus in Rhodobacter sphaeroides. I. Quinone domains and excitation transfer in chromatophores and reaction center.antenna complexes

The purpose of this study was to gain information on the functional consequences of the supramolecular organization of the photosynthetic apparatus in the bacterium Rhodobacter sphaeroides. Isolated complexes of the reaction center (RC) with its core antenna ring (light-harvesting complex 1 (LH1)) were studied in their dimeric (native) form or as monomers with respect to excitation transfer and distribution of the quinone pool. Similar issues were examined in chromatophore membranes. The relationship between the fluorescence yield and the amount of closed centers is indicative of a very efficient excitation transfer between the two monomers in isolated dimeric complexes. A similar dependence was observed in chromatophores, suggesting that excitation transfer in vivo from a closed RC.LH1 unit is also essentially directed to its partner in the dimer. The isolated complexes were found to retain 25-30% of the endogenous quinone acceptor pool, and the distribution of this pool among the complexes suggests a cooperative character for the association of quinones with the protein complexes. In chromatophores, the decrease in the amount of photoreducible quinones when inhibiting a fraction of the centers implies a confinement of the quinone pool over small domains, including one to six reaction centers. We suggest that the crowding of membrane proteins may not be the sole reason for quinone confinement and that a quinone-rich region is formed around the RC.LH1 complexes.     

X-ray diffraction studies on chromatophore membrane from photosynthetic bacteria. III. Basic structure of the photosynthetic unit and its relation to other bacteriochlorophyll forms

We have performed X-ray diffraction studies on photosynthetic units of Rhodospirillum rubrum and solubilized *B800 + B890 complex from chromatophores of Chromatium vinosum, to investigate the homology of their molecular structures. The native chromatophores of Chromatium vinosum, which contain other bacteriochlorophyll forms, were examined by an X-ray diffraction technique, in order to assess the interactions between the complexes as well as the molecular structures of the bacteriochlorophyll forms. The subchromatophore particles, solubilized by Triton X-100 from cells of Chromatium vinosum, exhibit a major absorption maximum at 881 nm and a minor one at 804 nm, consisting of bacteriochlorophyll form *B800 + B890. The near-IR absorption spectrum of the particle is very similar to that of chromatophores of Rhodospirillum rubrum although the major absorption maximum is shifted slightly. The X-ray diffraction pattern of the subchromatophore particles is very similar to that of chromatophores of Rhodospirillum rubrum. Thus, the subchromatophore particles are considered to be the "photoreaction unit" of Rhodospirillum rubrum. Since the bacteriochlorophyll form, *B800 + B890, is common in the purple bacteria, it is strongly suggested that the photoreaction unit is the basic and common structure existing in the photosynthetic units of purple bacteria. Chromatium vinosum cells exhibit different near-IR absorption spectra, depending on the culture media and also on the intensity of the illumination during culture. The chromatophores from these cells give different equatorial X-ray diffraction patterns. These patterns are much broader than that of solubilized subchromatophore particles, though they have common features. Thus, the molecular structures in the photosynthetic units are different, depending on their constituent bacteriochlorophyll forms.(ABSTRACT TRUNCATED AT 250 WORDS)     

Generation of electric current by chromatophores of Rhodospirillum rubrum and reconstitution of electrogenic function in subchromatophore pigment-protein complexes

Lipoprotein complexes, containing (1) bacteriochlorophyll reaction centers, (2) bacteriochlorophyll light-harvesting antenna or (3) both reaction centers and antenna, have been isolated from chromatophores of non-sulphur purple bacteria Rhodospirillum rubrum by detergent treatments. The method of reconstituting the proteoliposomes containing these complexes is described. Being associated with planar azolectin membrane, proteoliposomes as well as intact chromatophores were found to generate a light-dependent transmembrane electric potential difference measured by Ag/AgCl electrodes and voltmeter. The direction of the electric field in proteoliposomes can be regulated by the addition of antenna complexes to the reconstitution mixture. The reaction center complex proteoliposomes generate an electric field of a direction opposite to that in chromatophores, whereas proteoliposomes containing reaction center complexes and a sufficient amount of antenna complexes produce a potential difference as in chromatophores. ATP and inorganic pyrophosphate, besides light, were shown to be usable as energy sources for electric generation in chromatophores associated with planar membrane.     

The involvement of iron and ubiquinone in electron transfer reactions mediated by reaction centers from photosynthetic bacteria.

Reaction centers from Rhodopseudomonas sphaeroides strain R-26 were prepared with varying Fe and ubiquinone (Q) contents. The photooxidation of P-870 to P-870+ was found to occur with the same quantum yield in Fe-depleted reaction centers as in control samples. The kinetics of electron transfer from the initial electron acceptor (I) to Q also were unchanged upon Fe removal. We conclude that Fe has no measurable role in the primary photochemical reaction. The extent of secondary reaction from the first quinone acceptor (QA) to the second quinone acceptor (QB) was monitored by the decay kinetics of P-870+ after excitation of reaction centers with single flashes in the absence of electron donors, and by the amount of P-870 photooxidation that occurred on the second flash in the presence of electron donors. In reaction centers with nearly one iron and between 1 and 2 ubiquinones per reaction center, the amount of secondary electron transfer is proportional to the ubiquinone content above one per reaction center. In reaction centers treated with LiClO4 and o-phenanthroline to remove Fe, the amount of secondary reaction is decreased and is proportional to Fe content. Fe seems to be required for the secondary reaction. In reaction centers depleted of Fe by treatment with SDS and EDTA, the correlation between Fe content and secondary activity is not as good as that found using LiClO4. This is probably due in part to a loss of primary photochemical activity in samples treated with SDS; but the correlation is still not perfect after correction for this effect. The nature of the back reaction between P-870+ and Q-B was investigated using stopped flow techniques. Reaction centers in the P-870+ Q-B state decay with a 1-s half-time in both the presence and absence of o-phenanthroline, an inhibitor of electron transfer between Q-B and QB. This indicates that the back reaction between P-870+ and Q-A is direct, rather than proceeding via thermal repopulation of Q-A. The P-870+ Q-B state is calculated to lie at least 100 mV in free energy below the P-870+ Q-A state.     

Quinone Pathways in Entire Photosynthetic Chromatophores of Rhodospirillum photometricum

In photosynthetic organisms, membrane pigment-protein complexes [light-harvesting complex 1 (LH1) and light-harvesting complex 2 (LH2)] harvest solar energy and convert sunlight into an electrical and redox potential gradient (reaction center) with high efficiency. Recent atomic force microscopy studies have described their organization in native membranes. However, the cytochrome (cyt) bc₁ complex remains unseen, and the important question of how reduction energy can efficiently pass from core complexes (reaction center and LH1) to distant cyt bc₁ via membrane-soluble quinones needs to be addressed. Here, we report atomic force microscopy images of entire chromatophores of Rhodospirillum photometricum. We found that core complexes influence their molecular environment within a critical radius of ∼ 250 Å. Due to the size mismatch with LH2, lipid membrane spaces favorable for quinone diffusion are found within this critical radius around cores. We show that core complexes form a network throughout entire chromatophores, providing potential quinone diffusion pathways that will considerably speed the redox energy transfer to distant cyt bc₁. These long-range quinone pathway networks result from cooperative short-range interactions of cores with their immediate environment.     

Hydrogenase activity in Thiocapsa roseopersicina according to the D2--H20 metabolic reaction]

Extracts of Thiocapsa roseopersicina cells show hydrogenase activity, measured by evolution of H2 from reduced methylviologene (MV) and by D2-H2O exchange reaction. According to these reactions the most part of hydrogenases is found to be in the soluble fraction. Hydrogenase activity measured in the exchange reaction is completely inhibited by p-chloromercurybenzoate (5-10- minus 3 M), iodacetate (1-10- minus 2 M) and 26% inhibited by KCN and o-phenanthroline (5-10- minus 3 M). Evolution of H2 from reduced MV was not inhibited by o-phenanthroline, KCN and iodacetate and was inhibited by 66% only with p-chloromercurybenzoate. Light and ATP stimulated hydrogenase activity of chromatophores did not affect on its activity in the soluble fraction. The results obtained show that there are certain differences in hydrogenase systems responsible for the exchange reaction and evolution of H2.     

Kinetics of the generation of a photo-induced electric potential in chromatophores of photosynthetizing bacteria

Flash-induced formation of an electric potential difference (delta psi) was monitored by a direct method in chromatophores associated with the collodion phospholipid membrane. In Rhodospirillum rubrum and Rhodopseudomonas sphaeriodes chromatophores, the kinetics of delta psi generation exhibit fast (tau less than or equal to 0.3 microseconds) and slow (tau congruent to 200 microseconds) phases, the latter observed in the presence of exogenous quinones. Comparison of the kinetic and potentiometric characteristics of the process with those of electron transport reactions suggests that the fast phase of delta psi rise is due to charge separation between the primary electron donor, P870, and primary electron acceptor QIFe; the slow phase, which is inhibited by o-phenanthroline, is due to electron donation from QIFe to the secondary acceptor, quinone QII. The kinetics of delta psi decay include components arising form the recombination of primary separated charges (tau congruent to 30 ms) and from the passive discharge of the membrane (tau congruent to 400 ms; tau congruent to 1400 ms). From a redox titration of the photo-induced electric signal and the photo-induced absorption changes of P870 at different pH meanings, the value of pK for the primary acceptor FeQI was found to be 7.4 in Rps. sphaeroides chromatophores. In Chromatium minutissimum, a phase ( tau congruent to 20 microseconds) was observed in addition to those seen in Rps. sphaeroids and R. rubrum which was explained by the reduction of P890+ from the high potential cytochrome c555. Possible distribution of the electron transport components in the chromatophore membrane are discussed.     

Spectral and photochemical properties of subchromatophore fractions derived from carotenoid-deficient Chromatium by Triton treatment

Triton treatment of chromatophores of carotenoid-deficient Chromatium followed by density-gradient centrifugation led to a separation into three subchromatophore fractions. Unlike the case with chromatophores of regular Chromatium, Triton releases about 1/3 of the total bulk bacteriochlorophyll into one fraction (designated G, for green) whose major absorption-band maximum is at 780 nm. One fraction (H, for heavy) absorbs at 805 and 885 nm, with an absorbance ratio A₈₈₅ nm/A₈₀₅ nm between 1.5 and 2; another fraction (L, for light) absorbs at 805 nm and has a shoulder at 825 nm. The absorption and fluorescence emission spectra of the three fractions at room temperature and 77°K indicate that the different bacteriochlorophyll forms are efficiently separated by Triton treatment.

The reaction center P890 is concentrated exclusively in the H-fraction, at a level of 5–7% of the bulk bacteriochlorophyll. The solubilized bacteriochlorophyll absorbing at 780 nm can be totally and irreversibly bleached by 5 mM ferricyanide. The other bacteriochlorophyll forms in the H- and L-fractions are also irreversibly bleached by ferricyanide to variable extents. P890 is the only component that can be re-reduced by ascorbate after ferricyanide oxidation. The P890 content estimated by reversible chemical bleaching agrees well with that obtained by reversible light bleaching. The different bacteriochlorophyll forms, with the exception of the 780-nm absorbing form, are relatively stable toward light bleaching. Again, only P890 is reversibly bleached by light.

Cytochromes-555 and -553 are distributed in both the H-and L-fractions, but not in the solubilized-bacteriochlorophyll G-fraction. However, only cytochromes in the H-fraction which contains all of the P890 can undergo coupled oxidation. Excitation with 20-nsec ruby-laser pulses shows that cytochrome-555 can be oxidized in 2–3 μsec by photooxidized P890, indicating that necessary conformation for rapid electron transport is retained in the subchromatophore particles.

The data on fractionation and redox reactions obtained here, together with direct kinetic measurements recently reported in the literature lend further support to the view that oxidation of these two cytochromes is mediated by the same reaction center, P890.     

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.     

Primary and secondary electron transfer in hexane-solubilized proteolipid complexes of Rhodopseudomonas sphaeroides R-26

Primary electron transfer in hexane-solubilized reaction center proteolipid complexes is similar to that in detergent-solubilized reaction centers or chromatophores when diaminodurene is electron donor. Approximate values for the extinction coefficients of ubisemiquinone and the diaminodurene cation can be calculated. The primary and secondary quinone sites are dissimilar and results in only the transient formation of a semiquinone anion pair after two photochemical turnovers. One of the semiquinone anions decays rapidly, the remaining one and the diaminodurene cation have long lifetimes. Disproportionation between the semiquinone anions does not occur.