Purple Photosynthetic Bacterium Rhodospirillum Rubrum Research Articles

Intramolecular charge-transfer enhances energy transfer efficiency in carotenoid-reconstituted light-harvesting 1 complex of purple photosynthetic bacteria

In bacterial photosynthesis, the excitation energy transfer (EET) from carotenoids to bacteriochlorophyll a has a significant impact on the overall efficiency of the primary photosynthetic process. This efficiency can be enhanced when the involved carotenoid has intramolecular charge-transfer (ICT) character, as found in light-harvesting systems of marine alga and diatoms. Here, we provide insights into the significance of ICT excited states following the incorporation of a higher plant carotenoid, β-apo-8′-carotenal, into the carotenoidless light-harvesting 1 (LH1) complex of the purple photosynthetic bacterium Rhodospirillum rubrum strain G9+. β-apo-8′-carotenal generates the ICT excited state in the reconstituted LH1 complex, achieving an efficiency of EET of up to 79%, which exceeds that found in the wild-type LH1 complex.

Polarization angle dependence of stark absorption spectra of spirilloxanthin bound to the reconstituted LH1 complexes using LH1-subunits isolated from the purple photosynthetic bacterium Rhodospirillum rubrum.

Reconstituted LH1 complexes were prepared using the LH1 subunit-type complexes, isolated from the purple photosynthetic bacterium Rhodospirillum (Rs.) rubrum, and purified all-trans spirilloxanthin. Stark absorption spectra of spirilloxanthin bound to both the native and reconstituted LH1 complexes were compared in different polarization angles (χ) against the external electric field. From the polarization angle dependence of the Stark absorption spectra, two angles were determined in reference to the direction of transition dipole moment (m) of spirilloxanthin: one is the change in polarizability upon photoexcitation (Δα), θ(Δα) and the other is the change in static dipole moment upon photoexcitation (Δμ), θ(Δμ). Despite the symmetric molecular structure of all-trans spirilloxanthin, its Stark absorption spectra show pronounced values of Δμ. This large Δμ values essentially caused by the effect of induced dipole moment through Δα both in the cases for native and reconstituted LH1 complexes. However, slightly different values of θ(Δα) and θ(Δμ) observed for the native LH1 complex suggest that spirilloxanthin is asymmetrically distorted when bound to the native LH1 complex and gives rise to intrinsic Δμ value.

Changes in hydrogen production and polymer accumulation upon sulfur-deprivation in purple photosynthetic bacteria

The work investigated physiological conditions directing cellular metabolism toward either H2-production or storage polymer accumulation in purple photosynthetic bacteria. Hydrogen-producing cultures of the purple anoxygenic photosynthetic bacterium Rhodospirillum rubrum were resuspended in media lacking sulfur (S) nutrients. S-deprived cultures displayed lack of growth, cessation of bacteriochlorophyll and protein accumulation, and inhibition of H2 evolution. Cell volume increased substantially and large amounts of polymer were found to accumulate extracellularly. Poly-β-hydroxybutyrate (PHB) content increased about 3.5-fold within 24 h of S-deprivation. Most cells remained viable after 100 h of S-deprivation and cultures were capable of resuming growth and H2-production when supplemented with sulfate. Transcript levels, protein amount, and activity of the nitrogenase enzyme, which are responsible for H2-production, decreased with a halftime of about 15 h upon S-deprivation. In addition, the nitrogenase NifH subunits were modified by ADP-ribosylation, indicating post-translational inactivation. Comparative aconitase activity measurements of control and S-deprived cells failed to indicate a general stress to Fe–S proteins, as aconitase, a Fe–S protein in the citric acid cycle sensitive to oxidative stress, maintained activity throughout the course of the S-deprivation. In contrast to nifH transcriptional down-regulation, expression of cysK (encoding cysteine synthase) was upregulated in response to S-deprivation. The described physiology is not specific to R. rubrum, as Rhodobacter sphaeroides and Rhodopseudomonas palustris exhibited a similar response to S-deprivation. It is suggested that manipulation of the supply of S-nutrients may serve as a tool for the alternative production of H2 or PHB in purple photosynthetic bacteria, thus affording opportunities to design photobiological systems that serve in both energy conversion and storage processes.

Probing the Effect of the Binding Site on the Electrostatic Behavior of a Series of Carotenoids Reconstituted into the Light-Harvesting 1 Complex from Purple Photosynthetic Bacterium Rhodospirillum rubrum Detected by Stark Spectroscopy

Reconstitutions of the LH1 complexes from the purple photosynthetic bacterium Rhodospirillum rubrum S1 were performed with a range of carotenoid molecules having different numbers of C=C conjugated double bonds. Since, as we showed previously, some of the added carotenoids tended to aggregate and then to remain with the reconstituted LH1 complexes (Nakagawa, K.; Suzuki, S.; Fujii, R.; Gardiner, A.T.; Cogdell, R.J.; Nango, M.; Hashimoto, H. Photosynth. Res. 2008, 95, 339-344), a further purification step using a sucrose density gradient centrifugation was introduced to improve purity of the final reconstituted sample. The measured absorption, fluorescence-excitation, and Stark spectra of the LH1 complex reconstituted with spirilloxanthin were identical with those obtained with the native, spirilloxanthin-containing, LH1 complex of Rs. rubrum S1. This shows that the electrostatic environments surrounding the carotenoid and bacteriochlorophyll a (BChl a) molecules in both of these LH1 complexes were essentially the same. In the LH1 complexes reconstituted with either rhodopin or spheroidene, however, the wavelength maximum at the BChl a Qy absorption band was slightly different to that of the native LH1 complexes. These differences in the transition energy of the BChl a Qy absorption band can be explained using the values of the nonlinear optical parameters of this absorption band, i.e., the polarizability change Tr(Deltaalpha) and the static dipole-moment change |Deltamu| upon photoexcitation, as determined using Stark spectroscopy. The local electric field around the BChl a in the native LH1 complex (ES) was determined to be approximately 3.0x10(6) V/cm. Furthermore, on the basis of the values of the nonlinear optical parameters of the carotenoids in the reconstituted LH1 complexes, it is possible to suggest that the conformations of carotenoids, anhydrorhodovibrin and spheroidene, in the LH1 complex were similar to that of rhodopin glucoside in crystal structure of the LH2 complex from Rhodopseudomonas acidophila 10050.

Electrostatic effect of surfactant molecules on bacteriochlorophyll a and carotenoid binding sites in the LH1 complex isolated from Rhodospirillum rubrum S1 probed by Stark spectroscopy

The LH1 complexes were isolated from the purple photosynthetic bacterium Rhodospirillum rubrum strain S1. They were initially solubilized using LDAO and then purified in the presence of Triton X-100. The purified complexes were then either used directly or following an exchange into LDAO. Stark spectroscopy was applied to probe the electrostatic field around the bacteriochlorophyll a (BChl a) and carotenoid binding sites in the LH1 complexes surrounded by these two different surfactant molecules. Polarizabilty change (deltaalpha)) and dipole moment change (deltamicrom) upon photoexcitation were determined for the BChl a Q(y) band. Both of these parameters show smaller values in the presence of LDAO than in Triton X-100. This indicates that polar detergent molecules, like LDAO, affect the electrostatic environment around BChl a, and modify the nonlinear optical parameters (deltaalpha and deltamicrom values). The electrostatic field around the BChl a binding site, which is generated by the presence of LDAO, was determined to be |E ( L )| = approximately 3.9 x 10(5) [V/cm]. Interestingly, this kind of electrostatic effect was not observed for the carotenoid-binding site. The present study demonstrates a unique electrostatic interaction between the polar detergent molecules surrounding the LH1 complex and the Q(y) absorption band of BChl a that is bound to the LH1 complex.

H+‐PPases: yesterday, today and tomorrow

Suggestions by Calvin about a role of inorganic pyrophosphate (PPi) in early photosynthesis and by Lipmann that PPi may have been the original energy-rich phosphate donor in biological energy conversion, were followed in the mid-1960s by experimental results with isolated chromatophore membranes from the purple photosynthetic bacterium Rhodospirillum rubrum. PPi was shown to be hydrolysed in an uncoupler stimulated reaction by a membrane-bound inorganic pyrophosphatase (PPase), to be formed at the expense of light energy in photophosphorylation and to be utilized as an energy donor for various energy-requiring reactions, as a first known alternative to ATP. This direct link between PPi and photosynthesis led to increasing attention concerning the role of PPi in both early and present biological energy transfer. In the 1970s, the PPase was shown to be a proton pump and to be present also in higher plants. In the 1990s, sequences of H(+)-PPase genes were obtained from plants, protists, bacteria and archaea and two classes of H(+)-PPases differing in K(+) sensitivity were established. Over 200 H(+)-PPase sequences have now been determined. Recent biochemical and biophysical results have led to new progress and questions regarding the H(+)-PPase family, as well as the families of soluble PPases and the inorganic polyphosphatases, which hydrolyse inorganic linear high-molecular-weight polyphosphates (HMW-polyP). Here we will focus attention on the H(+)-PPases, their evolution and putative active site motifs, response to monovalent cations, genetic regulation and some very recent results, based on new methods for obtaining large quantities of purified protein, about their tertiary and quaternary structures.

Solution Structures of the Core Light-harvesting α and β Polypeptides from Rhodospirillum rubrum: Implications for the Pigment–Protein and Protein–Protein Interactions

We have determined the solution structures of the core light-harvesting (LH1) alpha and beta-polypeptides from wild-type purple photosynthetic bacterium Rhodospirillum rubrum using multidimensional NMR spectroscopy. The two polypeptides form stable alpha helices in organic solution. The structure of alpha-polypeptide consists of a long helix of 32 amino acid residues over the central transmembrane domain and a short helical segment at the N terminus that is followed by a three-residue loop. Pigment-coordinating histidine residue (His29) in the alpha-polypeptide is located near the middle of the central helix. The structure of beta-polypeptide shows a single helix of 32 amino acid residues in the membrane-spanning region with the pigment-coordinating histidine residue (His38) at a position close to the C-terminal end of the helix. Strong hydrogen bonds have been identified for the backbone amide protons over the central helical regions, indicating a rigid property of the two polypeptides. The overall structures of the R.rubrum LH1 alpha and beta-polypeptides are different from those previously reported for the LH1 beta-polypeptide of Rhodobacter sphaeroides, but are very similar to the structures of the corresponding LH2 alpha and beta-polypeptides determined by X-ray crystallography. A model constructed for the structural subunit (B820) of LH1 complex using the solution structures reveals several important features on the interactions between the LH1 alpha and beta-polypeptides. The significance of the N-terminal regions of the two polypeptides for stabilizing both B820 and LH1 complexes, as clarified by many experiments, may be attributed to the interactions between the short N-terminal helix (Trp2-Gln6) of alpha-polypeptide and a GxxxG motif in the beta-polypeptide.

Functional expression and characterization of a bacterial light-harvesting membrane protein in Escherichia coli and cell-free synthesis systems.

Heterologous expression of a bacterial light-harvesting (LH) integral membrane protein was attempted using Escherichia coli cells and cell-free synthesis systems prepared from E. coli extracts. The alpha-apoprotein of LH1 complex from purple photosynthetic bacterium Rhodospirillum rubrum was overexpressed as a recombinant protein with a histidine (His6) tag added to the carboxyl terminus. Both of the expression systems produced alpha-apoprotein in a fully functional form as can judged by its ability to form a structural subunit with native beta-apoprotein and the pigment molecule bacteriochlorophyll a. The expression product in E. coli appears to be located in the inner cell membrane and can be almost completely extracted by 0.5% (w/v) Triton X-100. Circular dichroism measurement indicated that the expressed alpha-apoproteins from both systems had alpha-helical contents essentially identical with that of the native one. About two thirds of the alpha-apoprotein expressed in E. coli was found to have the amino terminal methionine residue modified by a formyl group. About one third of the alpha-apoprotein expressed in the cell-free system was found to be oxidized at the side chain of the amino terminal methionine residue. Functional expression of the alpha-apoprotein using the cell-free system provides an useful example for producing highly hydrophobic integral membrane proteins with relatively large quantities sufficient for biophysical and structural analysis.

Methionine oxidation and its effect on the stability of a reconstituted subunit of the light-harvesting complex from Rhodospirillum rubrum.

An additional component in the purified core light-harvesting complex (LH1) from wild-type purple photosynthetic bacterium Rhodospirillum rubrum has been identified as an oxidized species of alpha-polypeptide by MALDI-TOF mass spectrometry. This component appears as a slightly earlier-eluting peak in the RP-HPLC chromatogram compared with the authentic alpha-polypeptide. The oxidation site has been determined to be the N-terminal methionine residue by high-resolution NMR spectroscopy, where the methionine is oxidized to methionine sulfoxide in a diastereoisomeric form. Interconversion between the oxidized and authentic alpha-polypeptides has been confirmed by selective oxidation and reduction. The oxidative modification of methionine is shown to have discernible effects on the ability to form B820 subunit with beta-polypeptide and bacteriochlorophyll a, and on the stability of the reconstituted B820 subunit. Both the ability and the stability for the samples using the oxidized alpha-polypeptide are moderately reduced, indicating that the oxidation-induced conformational change in the N-terminal domain of alpha-polypeptide may affect the pigment-binding environment through a long-range interaction. The MALDI-TOF mass results also reveal that the N-terminus of alpha-polypeptide is formylated and no phosphorylation has occurred in this polypeptide.

Energy transfer in the inhomogeneously broadened core antenna of purple bacteria: a simultaneous fit of low-intensity picosecond absorption and fluorescence kinetics

The excited state decay kinetics of chromatophores of the purple photosynthetic bacterium Rhodospirillum rubrum have been recorded at 77 K using picosecond absorption difference spectroscopy under strict annihilation free conditions. The kinetics are shown to be strongly detection wavelength dependent. A simultaneous kinetic modeling of these experiments together with earlier fluorescence kinetics by numerical integration of the appropriate master equation is performed. This model, which accounts for the spectral inhomogeneity of the core light-harvesting antenna of photosynthetic purple bacteria, reveals three qualitatively distinct stages of excitation transfer with different time scales. At first a fast transfer to a local energy minimum takes place (approximately 1 ps). This is followed by a much slower transfer between different energy minima (10-30 ps). The third component corresponds to the excitation transfer to the reaction center, which depends on its state (60 and 200 ps for open and closed, respectively) and seems also to be the bottleneck in the overall trapping time. An acceptable correspondence between theoretical and experimental decay kinetics is achieved at 77 K and at room temperature by assuming that the width of the inhomogeneous broadening is 10-15 nm and the mean residence time of the excitation in the antenna lattice site is 2-3 ps.

Kinetic model of primary energy transfer and trapping in photosynthetic membranes

The picosecond time-domain incoherent singlet excitation transfer and trapping kinetics in core antenna of photosynthetic bacteria are studied in case of low excitation intensities by numerical integration of the appropriate master equation in a wide temperature range of 4-300 K. The essential features of our two-dimensional-lattice model are as follows: Förster excitation transfer theory, spectral heterogeneity of both the light-harvesting antenna and the reaction center, treatment of temperature effects through temperature dependence of spectral bands, inclusion of inner structure of the trap, and transition dipole moment orientation. The fluorescence kinetics is analyzed in terms of distributions of various kinetic components, and the influence of different inhomogeneities (orientational, spectral) is studied.A reasonably good agreement between theoretical and experimental fluorescence decay kinetics for purple photosynthetic bacterium Rhodospirillum rubrum is achieved at high temperatures by assuming relatively large antenna spectral inhomogeneity: 20 nm at the whole bandwidth of 40 nm. The mean residence time in the antenna lattice site (it is assumed to be the aggregate of four bacteriochlorophyll a molecules bound to proteins) is estimated to be approximately 12 ps. At 4 K only qualitative agreement between model and experiment is gained. The failure of quantitative fitting is perhaps due to the lack of knowledge about the real structure of antenna or local heating and cooling effects not taken into account.

Picosecond fluorescence of simple photosynthetic membranes: Evidence of spectral inhomogeneity and directed energy transfer

The picosecond time-domain singlet excitation transfer and trapping kinetics in photosynthetic membranes in case of low excitation intensities is studied by numerical integration of the appropriate master equation. The essential features of our two-dimensional-lattice random walk model are spectral heterogeneity of the light-harvesting antenna, inclusion of temperature effects, nonabsolute excitation trap, correlation between spectral and spatial parameters. A reasonably good agreement between theoretical and experimental fluorescence decay kinetics for purple photosynthetic bacterium Rhodospirillum rubrum is achieved only by assuming relatively large spectral inhomogeneity. From this comparison the average excitation lifetime on the lattice site is estimated to be 5–8 ps at the effective nearest neighbour lattice distance of 32 Å. If the model is correct, the relatively slow hopping rate determines that excitation transfer and trapping in R. rubrum at active photosynthesis conditions is a diffusion-limited process. The invariably present spectral disorder of photosynthetic systems promoting directed energy transfer serves for higher light-utilizing efficiency.

Molecular cloning, sequencing and expression of cytochrome c2 from Rhodospirillum rubrum

Cytochrome c2 (Mr 12,840) of the purple photosynthetic bacterium Rhodospirillum rubrum functions as a mobile electron carrier in the cyclic photosynthetic electron-transport system of this organism. It acts as the electron donor to photochemically oxidized reaction centres and is reduced in turn by electrons from the cytochrome bc1 complex. By using synthetic oligonucleotides based on the known amino acid sequence of the protein, the structural gene (cycA) has been identified and isolated. DNA sequence analysis indicates the presence of a typical prokaryotic 23-residue signal sequence, suggesting that the protein is synthesized as a precursor which is processed during its secretion into the periplasm. Evidence is presented for the production of assembled cytochrome c2 in Escherichia coli, but recombinants grow poorly and are unstable, suggesting toxicity of the gene product in this organism.

Substrate specificity and regulation of the maize (Zea mays) leaf ADP: protein phosphotransferase catalysing phosphorylation/inactivation of pyruvate, orthophosphate dikinase.

The protein substrate specificity of the maize (Zea mays) leaf ADP: protein phosphotransferase (regulatory protein, RP) was studied in terms of its relative ability to inactivate/phosphorylate pyruvate, orthophosphate dikinase from Zea mays and the non-sulphur purple photosynthetic bacterium Rhodospirillum rubrum. The dimeric bacterial dikinase was inactivated by the maize leaf RP via phosphorylation, with a stoichiometry of approximately 1 mol of phosphate incorporated/mol of 92.7-kDa protomer. Inactivation required both ADP and ATP, with ADP being the specific donor for regulatory phosphorylation. The requirements for inactivation/phosphorylation in this heterologous system were identical with those previously established for the tetrameric maize leaf dikinase. The ADP-dependent maize leaf RP did not phosphorylate alternative protein substrates such as casein or phosvitin, and its activity was not affected by cyclic nucleotides, Ca2+ or calmodulin. The regulation of the maize leaf ADP: protein phosphotransferase was studied in terms of changes in adenylate energy charge and pyruvate concentration. The change in adenylate energy charge necessary to substantially inhibit phosphorylation of maize leaf dikinase was not suggestive of it being a physiological modulator of phosphotransferase activity. Pyruvate was a potent competitive inhibitor of regulatory phosphorylation (Ki = 80 microM), consistent with its interaction with the catalytic phosphorylated intermediate of dikinase, the true protein substrate for ADP-dependent phosphorylation/inactivation.

Partial purification and characterization of pyruvate, orthophosphate dikinase from Rhodospirillum rubrum.

We confirmed an earlier report (B. B. Buchanan, J. Bacteriol. 119:1066-1068, 1974) that the nonsulfur purple photosynthetic bacterium Rhodospirillum rubrum contains pyruvate, orthophosphate dikinase (EC 2.7.9.1) activity that is absolutely dependent upon all three substrates by performing enzyme assays in both the forward (phosphoenolpyruvate formation) and reverse (ATP formation) directions. Of the various carbon sources tested, photoheterotrophic growth on DL-lactate plus bicarbonate proved to be best for the production of dikinase activity units. A four-step protocol, which included batch DEAE-cellulose processing, ammonium sulfate fractionation, and chromatography on hydroxylapatite and Blue A Dyematrex gels, was devised for partially purifying the enzyme from such cells. The protein was purified about 80-fold to an apparent electrophoretic purity of about 60% and a final specific activity of 3.6 U/mg of protein, with about a 35% overall recovery of activity units. Estimations of native and monomeric relative molecular weights by sucrose density gradient centrifugation, high-pressure liquid chromatography-based size exclusion chromatography, denaturing electrophoresis, and immunoblotting suggested that the holoenzyme was most likely a homodimer of 92.7-kilodalton subunits. The results are compared with related previous data on the nonphotosynthetic bacterial dikinase and the C4 mesophyll chloroplast enzyme.

The structure of oxidized cytochrome c 2 of Rhodospirillum rubrum.

Abstract The structure of ferricytochrome c2 from the non-sulfur purple photosynthetic bacterium Rhodospirillum rubrum has been determined at 2 A resolution by x-ray crystallographic methods. The 112-residue polypeptide chain encloses a single covalently bound heme in a predominantly hydrophobic environment, leaving only one edge exposed to the solvent at the front of the molecule. Distributed around the exterior perimeter of the heme crevice are 11 lysine residues which form an essentially uninterrupted positively charged patch. The molecule contains four segments of α-helix, with the conformation of the remainder of the chain being primarily governed by interactions with the heme. A hypothetical scheme for folding of the molecule is presented, based primarily upon the assumption that the helical regions are formed first and are subsequently distorted by hydrophobic interactions with the heme. The heme iron is coordinated to nitrogen Ne2 of His 18 and to the sulfur atom of Met 91 in the fifth and sixth positions. A notable feature of the structure is an apparently "off axis" or bent Met 91 sulfur-iron bond. The non-axial nature of this bond is attributed to a charge-pair interaction between the Tyr 70 hydroxyl oxygen, bearing a partial negative charge, and the Met 91 sulfur atom, bearing a partial positive charge delocalized from the ferriheme iron. This interaction serves to stabilize the oxidized heme. The additional participation of Tyr 70 in a hydrogen bond network via Tyr 52 to Ser 89 on the front surface of the molecule suggests that the physiological mechanism for reduction of cytochrome c2 involves concerted protonation of Ser 89 concomitant with electron donation to the heme. The process is reversed for oxidation. This proposed mechanism has several chemical and structural implications, the most important being that the site of interaction with physiological oxido-reductants is at the front of the cytochrome c2 molecule. These conclusions appear to be substantiated by a variety of published findings, including pH dependence of the midpoint potential of cytochrome c2 and polylysine inhibition of cytochrome c2 reactivity in physiological oxidation-reduction systems.

Amino acid sequence of cytochrome c' from the purple photosynthetic bacterium Rhodospirillum rubrum S1.

The amino acid sequence of cytochrome c' from the purple photosynthetic bacterium Rhodospirillum rubrum S1 has been determined and is consistent with homology to cytochrome c' from the nonphotosynthetic bacterium Alcaligenes sp. NCIB 11015. There is 29% identity in the chosen alignment of these two proteins. R. rubrum cytochrome c' is composed of a single peptide chain of 126 amino acid residues with a single heme covalently bound near the COOH terminus. There is no sequence similarity to mitochondrial cytochrome c, except at the heme binding site.

Glycollate formation and excretion by the purple photosynthetic bacterium Rhodospirillum rubrum

Glycollate formation and excretion by the purple photosynthetic bacterium Rhodospirillum rubrum

Regulation of the cytoplasmic inorganic pyrophosphatase of Rhodospirillum rubrum.

This study is concerned with the catalytic and regulatory properties of soluble inorganic pyrophosphatase of the nonsulfur purple photosynthetic bacterium Rhodospirillum rubrum. A procedure is described for reproducible 100‐fold purification of the enzyme, which shows complex kinetic behavior. Free Mg2+ is an activator of the pyrophosphatase, and virtually eliminates the sigmoidicity otherwise observed in the substrate (magnesium pyrophosphate) saturation kinetic curves. In the absence of appreciable free Mg2+, the enzyme is inhibited by 2‐phosphoglyceric acid, which has the effect of increasing the [S]0.5 value (substrate concentration required for half‐maximal velocity) and of decreasing V. The pyrophosphatase, in dilute solution, is slowly inactivated when the pH is less than 8.6, and this is specifically prevented by Zn2+. Inactivation caused by exposure to low pH (7.6–8.2) can be reversed partially by addition of Zn2+ and/or exposure to high pH (9–9.5). Full reactivation can be achieved by proper adjustment of pH and Zn2+ concentration, together with addition of a reductant (dithionite). The pH‐induced inactivation is accelerated by nucleoside triphosphates, reduced pyridine nucleotides, and the allosteric inhibitor, 2‐phosphoglyceric acid. Such inactivations are reversible, and are not accompanied by change in molecular weight of the enzyme (∼100000). It appears that the R. rubrum inorganic pyrophosphatase can exist in several interconvertible states, which are characterized by inherently different specific activities. Transitions between alternative states are influenced by the various chemical modifiers and conditions noted, and the phenomena described provide a basis for further investigation of the mechanisms responsible for regulation of the enzyme's activity.

Photosynthetic electron transport induced by flashing light in the purple photosynthetic bacterium Rhodospirillum rubrum

Photosynthetic electron transport induced by flashing light in the purple photosynthetic bacterium Rhodospirillum rubrum