Photoproduction of Hydrogen by Purple Bacteria: A Critical Evaluation of the Rate Limiting Enzymatic Steps

1993 ◽  
Vol 48 (5-6) ◽  
pp. 482-487 ◽  
Author(s):  
J.-H. Klemme
Keyword(s):  
Hydrogen Transfer ◽  
Rhodospirillum Rubrum ◽  
Purple Bacteria ◽  
Bacterial Species ◽  
Critical Evaluation ◽  
Reducing Power ◽  
Organic Substrate ◽  
Organic C ◽  
Rate Limiting

Abstract The enzymatic mechanisms and energetics of nitrogenase-catalyzed photoproduction of hydrogen from organic C-compounds by purple bacteria are discussed in respect to the question of which of the following three enzymes or enzyme systems are rate limiting for H2-production: (a) the nitrogenase-complex; (b) the enzymes and electron transport proteins involved in hydrogen transfer from the organic substrate(s) to nitrogenase; and (c) the system of photosynthetic ATP-regeneration. Calculations of maximum in vivo rates of photosynthetic ATPregeneration (gATP-values derived from growth rates), and of ATP-consumption by nitrogenase- catalyzed H2-production, and comparison of these rates with the specific activities of the enzymes of hydrogen or electron transfer from the C-substrate to the nitrogenase-complex, make it very likely that, in Rhodospirillum rubrum, nitrogenase-catalyzed H2-formation is limited by the availability of ATP and, possibly, of reducing power. In two other nonsulfur purple bacterial species (Rhodobacter capsulatus and Rhodobacter sphaeroides), H2-photoproduction is probably not energy-limited.

scholarly journals Determining the Rate-Limiting Step for Light-Responsive Redox Regulation in Chloroplasts

Antioxidants ◽  
2018 ◽  
Vol 7 (11) ◽  
pp. 153 ◽  
Author(s):  
Keisuke Yoshida ◽  
Toru Hisabori
Keyword(s):  
Redox Regulation ◽  
Reducing Power ◽  
Rubisco Activase ◽  
Power Transfer ◽  
Target Proteins ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Thiol-based redox regulation ensures light-responsive control of chloroplast functions. Light-derived signal is transferred in the form of reducing power from the photosynthetic electron transport chain to several redox-sensitive target proteins. Two types of protein, ferredoxin-thioredoxin reductase (FTR) and thioredoxin (Trx), are well recognized as the mediators of reducing power. However, it remains unclear which step in a series of redox-relay reactions is the critical bottleneck for determining the rate of target protein reduction. To address this, the redox behaviors of FTR, Trx, and target proteins were extensively characterized in vitro and in vivo. The FTR/Trx redox cascade was reconstituted in vitro using recombinant proteins from Arabidopsis. On the basis of this assay, we found that the FTR catalytic subunit and f-type Trx are rapidly reduced after the drive of reducing power transfer, irrespective of the presence or absence of their downstream target proteins. By contrast, three target proteins, fructose 1,6-bisphosphatase (FBPase), sedoheptulose 1,7-bisphosphatase (SBPase), and Rubisco activase (RCA) showed different reduction patterns; in particular, SBPase was reduced at a low rate. The in vivo study using Arabidopsis plants showed that the Trx family is commonly and rapidly reduced upon high light irradiation, whereas FBPase, SBPase, and RCA are differentially and slowly reduced. Both of these biochemical and physiological findings suggest that reducing power transfer from Trx to its target proteins is a rate-limiting step for chloroplast redox regulation, conferring distinct light-responsive redox behaviors on each of the targets.

scholarly journals High-Level Production of the Industrial Product Lycopene by the Photosynthetic Bacterium Rhodospirillum rubrum

2012 ◽  
Vol 78 (20) ◽  
pp. 7205-7215 ◽  
Author(s):  
Guo-Shu Wang ◽  
Hartmut Grammel ◽  
Khaled Abou-Aisha ◽  
Rudolf Sägesser ◽  
Robin Ghosh
Keyword(s):  
Rhodospirillum Rubrum ◽  
Purple Bacteria ◽  
Dry Weight ◽  
Photosynthetic Bacterium ◽  
Downstream Processing ◽  
Kanamycin Resistance ◽  
Content Type ◽  
Light Harvesting Complex ◽  
Kanamycin Resistance Cassette

ABSTRACTThe biosynthesis of the major carotenoid spirilloxanthin by the purple nonsulfur bacteriumRhodospirillum rubrumis thought to occur via a linear pathway proceeding through phytoene and, later, lycopene as intermediates. This assumption is based solely on early chemical evidence (B. H. Davies, Biochem. J. 116:93–99, 1970). In most purple bacteria, the desaturation of phytoene, catalyzed by the enzyme phytoene desaturase (CrtI), leads to neurosporene, involving only three dehydrogenation steps and not four as in the case of lycopene. We show here that the chromosomal insertion of a kanamycin resistance cassette into thecrtC-crtDregion of the partial carotenoid gene cluster, whose gene products are responsible for the downstream processing of lycopene, leads to the accumulation of the latter as the major carotenoid. We provide spectroscopic and biochemical evidence thatin vivo, lycopene is incorporated into the light-harvesting complex 1 as efficiently as the methoxylated carotenoids spirilloxanthin (in the wild type) and 3,4,3′,4′-tetrahydrospirilloxanthin (in acrtDmutant), both under semiaerobic, chemoheterotrophic, and photosynthetic, anaerobic conditions. Quantitative growth experiments conducted in dark, semiaerobic conditions, using a growth medium for high cell density and high intracellular membrane levels, which are suitable for the conventional industrial production in the absence of light, yielded lycopene at up to 2 mg/g (dry weight) of cells or up to 15 mg/liter of culture. These values are comparable to those of many previously describedEscherichia colistrains engineered for lycopene production. This study provides the first genetic proof that theR. rubrumCrtI produces lycopene exclusively as an end product.

scholarly journals A CRITICAL EVALUATION OF THE HISTOCHEMICAL METHODS FOR CARBONIC ANHYDRASE

1972 ◽  
Vol 20 (5) ◽  
pp. 319-330 ◽  
Author(s):  
THOMAS F. MUTHER
Keyword(s):  
Enzyme Activity ◽  
Surface Layer ◽  
Carbonic Anhydrase ◽  
Sodium Lauryl Sulfate ◽  
Critical Evaluation ◽  
Lauryl Sulfate ◽  
Carbonic Anhydrase Inhibitors ◽  
Histochemical Methods ◽  
Rate Limiting

The histochemical methods for carbonic anhydrase are not based on the postulated dehydration of HCO3–. The staining is caused by the formation of an unknown reactive Co compound in the surface layer secondary to enzyme-independent alkalinization of the medium. Kinetic analysis of the reaction shows that loss of CO2 from the medium is rate-limiting. Carbonic anhydrase inhibitors delay the staining by interacting with Co and not by inhibiting the enzyme; they are effective when used after the reaction is complete. The reaction can also be inhibited by agents which are not carbonic anhydrase inhibitors, such as sodium lauryl sulfate and 5-aminothiadiazole, but not by in vivo administered acetazolamide. A comparison of the effect of various fixatives on the biochemical and histochemical enzyme activity shows no correlation. While carbonic anhydrase itself is stained by the reaction, the methods lack the claimed specificity for it.

scholarly journals Hydrogen transfer between ethanol molecules during oxidoreduction in vivo

1985 ◽  
Vol 229 (2) ◽  
pp. 315-322 ◽  
Author(s):  
T Cronholm
Keyword(s):  
Alcohol Dehydrogenase ◽  
Isotope Effect ◽  
Hydrogen Transfer ◽  
Ethanol Oxidation ◽  
Internal Standard ◽  
Ethanol Metabolism ◽  
Acetaldehyde Oxidation ◽  
Extensive Formation ◽  
Rate Limiting

Rates of exchange catalysed by alcohol dehydrogenase were determined in vivo in order to find rate-limiting steps in ethanol metabolism. Mixtures of [1,1-2H2]- and [2,2,2-2H3]ethanol were injected in rats with bile fistulas. The concentrations in bile of ethanols having different numbers of 2H atoms were determined by g.l.c.-m.s. after the addition of [2H6]ethanol as internal standard and formation of the 3,5-dinitrobenzoates. Extensive formation of [2H4]ethanol indicated that acetaldehyde formed from [2,2,2-2H3]ethanol was reduced to ethanol and that NADH used in this reduction was partly derived from oxidation of [1,1-2H2]ethanol. The rate of acetaldehyde reduction, the degree of labelling of bound NADH and the isotope effect on ethanol oxidation were calculated by fitting models to the found concentrations of ethanols labelled with 1-42H atoms. Control experiments with only [2,2,2-2H3]ethanol showed that there was no loss of the C-2 hydrogens by exchange. The isotope effect on ethanol oxidation appeared to be about 3. Experiments with (1S)-[1-2H]- and [2,2,2-2H3]ethanol indicated that the isotope effect on acetaldehyde oxidation was much smaller. The results indicated that both the rate of reduction of acetaldehyde and the rate of association of NADH with alcohol dehydrogenase were nearly as high as or higher than the net ethanol oxidation. Thus, the rate of ethanol oxidation in vivo is determined by the rates of acetaldehyde oxidation, the rate of dissociation of NADH from alcohol dehydrogenase, and by the rate of reoxidation of cytosolic NADH. In cyanamide-treated rats, the elimination of ethanol was slow but the rates in the oxidoreduction were high, indicating more complete rate-limitation by the oxidation of acetaldehyde.

Structural analysis of the photosynthetic membrane from Ectothiorhodospira halochloris

1983 ◽  
Vol 41 ◽  
pp. 740-741
Author(s):  
H. Engelhardt ◽  
R. Guckenberger ◽  
W. Baumeister
Keyword(s):  
Lattice Structure ◽  
Bacterial Species ◽  
Hexagonal Lattice ◽  
Reaction Centre ◽  
Photosynthetic Membrane ◽  
Rhodopseudomonas Viridis ◽  
Photosynthetic Membranes ◽  
Ectothiorhodospira Halochloris ◽  
Main Components

Bacterial photosynthetic membranes contain, apart from lipids and electron transport components, reaction centre (RC) and light harvesting (LH) polypeptides as the main components. The RC-LH complexes in Rhodopseudomonas viridis membranes are known since quite seme time to form a hexagonal lattice structure in vivo; hence this membrane attracted the particular attention of electron microscopists. Contrary to previous claims in the literature we found, however, that 2-D periodically organized photosynthetic membranes are not a unique feature of Rhodopseudomonas viridis. At least five bacterial species, all bacteriophyll b - containing, possess membranes with the RC-LH complexes regularly arrayed. All these membranes appear to have a similar lattice structure and fine-morphology. The lattice spacings of the Ectothiorhodospira haloohloris, Ectothiorhodospira abdelmalekii and Rhodopseudomonas viridis membranes are close to 13 nm, those of Thiocapsa pfennigii and Rhodopseudomonas sulfoviridis are slightly smaller (∼12.5 nm).

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Production of Novel Bioactive Compounds by the Bacteria Associated with Some Marine Sponges of Gulf of Mannar and Palk Bay, Southeast Coast of India

2018 ◽  
Vol 6 (8) ◽  
pp. 183
Author(s):  
V. Ramadas ◽  
G. Chandralega
Keyword(s):  
Bioactive Compounds ◽  
Bacterial Species ◽  
Marine Sponges ◽  
Marine Organisms ◽  
Gulf Of Mannar ◽  
Bacterial Symbionts ◽  
Palk Bay ◽  
Excellent Source

Sponges, exclusively are aquatic and mostly marine, are found from the deepest oceans to the edge of the sea. There are approximately 15,000 species of sponges in the world, of which, 150 occur in freshwater, but only about 17 are of commercial value. A total of 486 species of sponges have been identified in India. In the Gulf of Mannar and Palk Bay a maximum of 319 species of sponges have been recorded. It has been proved that marine organisms are excellent source of bioactive secondary metabolites and number of compounds of originated from marine organisms had been reported to possess in-vitro and in-vivo immuno stimulatory activity. Extracts from 20 sponge species were tested for bacterial symbionts and bioactive compounds were isolated from such associated bacterial species in the present study.

Cobalt/Lewis Acid Catalysis for Hydrocarbofunctionalization of Alkynes via Cooperative C–H Activation

2020 ◽  
Author(s):  
Chang-Sheng Wang ◽  
Sabrina Monaco ◽  
Anh Ngoc Thai ◽  
Md. Shafiqur Rahman ◽  
Chen Wang ◽  
...  
Keyword(s):  
Catalytic System ◽  
Lewis Acid ◽  
Hydrogen Transfer ◽  
Acid Catalysis ◽  
Rate Limiting Step ◽  
Site Selectivity ◽  
Set Up ◽  
Site Selective ◽  
First Time ◽  
Rate Limiting

A catalytic system comprised of a cobalt-diphosphine complex and a Lewis acid (LA) such as AlMe3 has been found to promote hydrocarbofunctionalization reactions of alkynes with Lewis basic and electron-deficient substrates such as formamides, pyridones, pyridines, and azole derivatives through site-selective C-H activation. Compared with known Ni/LA catalytic system for analogous transformations, the present catalytic system not only feature convenient set up using inexpensive and bench-stable precatalyst and ligand such as Co(acac)3 and 1,3-bis(diphenylphosphino)propane (dppp), but also display distinct site-selectivity toward C-H activation of pyridone and pyridine derivatives. In particular, a completely C4-selective alkenylation of pyridine has been achieved for the first time. Mechanistic stidies including DFT calculations on the Co/Al-catalyzed addition of formamide to alkyne have suggested that the reaction involves cleavage of the carbamoyl C-H bond as the rate-limiting step, which proceeds through a ligand-to-ligand hydrogen transfer (LLHT) mechanism leading to an alkyl(carbamoyl)cobalt intermediate.

Antioxidant Activity, Phenolic Content and Hematoprotective Effects of Cleome arabica Polyphenolic Leaf Extract

2019 ◽  
Author(s):  
C. Tigrine ◽  
A. Kameli
Keyword(s):  
Antioxidant Activity ◽  
Biological Effects ◽  
Reducing Power ◽  
Hematological Toxicity ◽  
Protective Effects ◽  
Ferrous Ions ◽  
Polyphenolic Extract ◽  
Cleome Arabica

In this study a polyphenolic extract from Cleome arabica leaves (CALE) was investigated for its antioxidant activity in vitro using DPPH•, metal chelating and reducing power methods and for its protective effects against AraC-induced hematological toxicity in vivo using Balb C mice. Results indicated that CALE exhibited a strong and dose-dependent scavenging activity against the DPPH• free radical (IC50 = 4.88 μg/ml) and a high reducing power activity (EC50 = 4.85 μg/ml). Furthermore, it showed a good chelating effects against ferrous ions (IC50 = 377.75 μg/ml). The analysis of blood showed that subcutaneous injection of AraC (50 mg/kg) to mice during three consecutive days caused a significant myelosupression (P < 0.05). The combination of CALE and AraC protected blood cells from a veritable toxicity. Where, the number of the red cells, the amount of hemoglobin and the percentage of the hematocrite were significantly high. On the other hand, AraC cause an elevation of body temperature (39 °C) in mice. However, the temperature of the group treated with CALE and AraC remained normal and did not exceed 37.5 °C. The observed biological effects of CALE, in vitro as well as in vivo, could be due to the high polyphenol and flavonoid contents. In addition, the antioxidant activity of CALE suggested to be responsible for its hematoprotective effect.

Oscillating conditions for influencing the composition of mixed biological cultures

1998 ◽  
Vol 37 (4-5) ◽  
pp. 259-262 ◽  
Author(s):  
Bjarne R. Horntvedt ◽  
Morten Rambekk ◽  
Rune Bakke
Keyword(s):  
Growth Rate ◽  
Specific Growth ◽  
Heterotrophic Bacteria ◽  
Bacterial Species ◽  
Rate Reduction ◽  
Similar Strategy ◽  
Sinusoidal Oscillations ◽  
Specific Growth Rates ◽  
Rate Limiting ◽  
Concentration Levels

This paper presents a strategy in which mixed biological cultures are exposed to oscillating concentration levels, to improve the potential for coexistence of desired bacterial species. A mechanistic mathematical model is constructed to investigate and illustrate this strategy. This paper is focused on competition between nitrifying, denitrifying and aerobic heterotrophic bacteria in a CSTR with sludge recycle. For nitrifying and aerobic heterotrophic cultures, the effect of sinusoidal oscillations in DO levels with an amplitude of 1.0 mg/l is a 16% specific growth rate reduction compared to that at a constant DO level. The denitrifiers growth rate is increased by an average of 59%, compared to the constant DO level situation. A similar strategy has been tested in a pilot plant. It is concluded that the influence on specific growth rates is a function of the amplitude of the oscillations. The effects are greatest when concentrations fluctuate around the half saturation concentration of the rate limiting component(s).

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