scholarly journals Catalytic reaction of cytokinin dehydrogenase: preference for quinones as electron acceptors

2004 ◽  
Vol 380 (1) ◽  
pp. 121-130 ◽  
Author(s):  
Jitka FRÉBORTOVÁ ◽  
Marco W. FRAAIJE ◽  
Petr GALUSZKA ◽  
Marek ŠEBELA ◽  
Pavel PEČ ◽  
...  
Keyword(s):  
Electron Acceptor ◽  
Catalytic Reaction ◽  
Oxidative Degradation ◽  
Reaction Rates ◽  
Electron Acceptors ◽  
Cytokinin Oxidase ◽  
Turnover Rates ◽  
Isopentenyl Adenine ◽  
Covalently Linked ◽  
Strict Specificity

The catalytic reaction of cytokinin oxidase/dehydrogenase (EC 1.5.99.12) was studied in detail using the recombinant flavoenzyme from maize. Determination of the redox potential of the covalently linked flavin cofactor revealed a relatively high potential dictating the type of electron acceptor that can be used by the enzyme. Using 2,6-dichlorophenol indophenol, 2,3-dimethoxy-5-methyl-1,4-benzoquinone or 1,4-naphthoquinone as electron acceptor, turnover rates with N6-(2-isopentenyl)adenine of approx. 150 s−1 could be obtained. This suggests that the natural electron acceptor of the enzyme is quite probably a p-quinone or similar compound. By using the stopped-flow technique, it was found that the enzyme is rapidly reduced by N6-(2-isopentenyl)adenine (kred=950 s−1). Re-oxidation of the reduced enzyme by molecular oxygen is too slow to be of physiological relevance, confirming its classification as a dehydrogenase. Furthermore, it was established for the first time that the enzyme is capable of degrading aromatic cytokinins, although at low reaction rates. As a result, the enzyme displays a dual catalytic mode for oxidative degradation of cytokinins: a low-rate and low-substrate specificity reaction with oxygen as the electron acceptor, and high activity and strict specificity for isopentenyladenine and analogous cytokinins with some specific electron acceptors.

The influence of potassium dichromate on dissimilatory reduction of sulfate and nitrate ions by bacteria Desulfovibrio sp.

2017 ◽  
Vol 28 (1-2) ◽  
pp. 84-95
Author(s):  
O. M. Moroz ◽  
S. O. Hnatush ◽  
Ch. I. Bohoslavets ◽  
T. M. Hrytsun’ ◽  
B. M. Borsukevych
Keyword(s):  
Electron Acceptor ◽  
Potassium Dichromate ◽  
Anaerobic Respiration ◽  
Sulfate Reducing Bacteria ◽  
Negative Influence ◽  
Electron Acceptors ◽  
Metal Compounds ◽  
Nitrate Ions ◽  
Sulfate Reducing ◽  
Reducing Bacteria

Sulfate reducing bacteria, capable to reductive transformation of different nature pollutants, used in biotechnologies of purification of sewage, contaminated by carbon, sulfur, nitrogen and metal compounds. H2S formed by them sediment metals to form of insoluble sulfides. Number of metals can be used by these microorganisms as electron acceptors during anaerobic respiration. Because under the influence of metal compounds observed slowing of bacteria metabolism, selection isolated from technologically modified ecotops resistant to pollutions strains is important task to create a new biotechnologies of purification. That’s why the purpose of this work was to study the influence of potassium dichromate, present in medium, on reduction of sulfate and nitrate ions by sulfate reducing bacteria Desulfovibrio desulfuricans IMV K-6, Desulfovibrio sp. Yav-6 and Desulfovibrio sp. Yav-8, isolated from Yavorivske Lake, to estimate the efficiency of possible usage of these bacteria in technologies of complex purification of environment from dangerous pollutants. Bacteria were cultivated in modified Kravtsov-Sorokin medium without SO42- and FeCl2×4H2O for 10 days. To study the influence of K2Cr2O7 on usage by bacteria SO42- or NO3- cells were seeded to media with Na2SO4×10H2O or NaNO3 and K2Cr2O7 at concentrations of 1.74 mM for total content of electron acceptors in medium 3.47 mM (concentration of SO42- in medium of standard composition). Cells were also seeded to media with 3.47 mM Na2SO4×10H2O, NaNO3 or K2Cr2O7 to investigate their growth in media with SO42-, NO3- or Cr2O72- as sole electron acceptor (control). Biomass was determined by turbidymetric method, content of sulfate, nitrate, dichromate, chromium (III) ions, hydrogen sulfide or ammonia ions in cultural liquid – by spectrophotometric method. It was found that K2Cr2O7 inhibits growth (2.2 and 1.3 times) and level of reduction by bacteria sulfate or nitrate ions (4.2 and 3.0 times, respectively) at simultaneous addition into cultivation medium of 1.74 mM SO42- or NO3- and 1.74 mM Cr2O72-, compared with growth and level of reduction of sulfate or nitrate ions in medium only with SO42- or NO3- as sole electron acceptor. Revealed that during cultivation of bacteria in presence of equimolar amount of SO42- or NO3- and Cr2O72-, last used by bacteria faster, content of Cr3+ during whole period of bacteria cultivation exceeded content H2S or NH4+. K2Cr2O7 in medium has most negative influence on dissimilatory reduction by bacteria SO42- than NO3-, since level of nitrate ions reduction by cells in medium with NO3- and Cr2O72- was a half times higher than level of sulfate ions reduction by it in medium with SO42- and Cr2O72-. The ability of bacteria Desulfovibrio sp. to priority reduction of Cr2O72- and after their exhaustion − NO3- and SO42- in the processes of anaerobic respiration can be used in technologies of complex purification of environment from toxic compounds.

scholarly journals Dehalogenation of the Herbicides Bromoxynil (3,5-Dibromo-4-Hydroxybenzonitrile) and Ioxynil (3,5-Diiodino-4-Hydroxybenzonitrile) by Desulfitobacterium chlororespirans

2005 ◽  
Vol 71 (7) ◽  
pp. 3741-3746 ◽  
Author(s):  
Alison M. Cupples ◽  
Robert A. Sanford ◽  
Gerald K. Sims
Keyword(s):  
Electron Acceptor ◽  
Pure Culture ◽  
Electron Acceptors ◽  
Reductive Dehalogenation ◽  
First Report ◽  
Lactate Uptake ◽  
Standard Deviations ◽  
Doubling Times

ABSTRACT Desulfitobacterium chlororespirans has been shown to grow by coupling the oxidation of lactate to the metabolic reductive dehalogenation of ortho chlorines on polysubstituted phenols. Here, we examine the ability of D. chlororespirans to debrominate and deiodinate the polysubstituted herbicides bromoxynil (3,5-dibromo-4-hydroxybenzonitrile), ioxynil (3,5-diiodo-4-hydroxybenzonitrile), and the bromoxynil metabolite 3,5-dibromo-4-hydroxybenzoate (DBHB). Stoichiometric debromination of bromoxynil to 4-cyanophenol and DBHB to 4-hydroxybenzoate occurred. Further, bromoxynil (35 to 75 μM) and DBHB (250 to 260 μM) were used as electron acceptors for growth. Doubling times for growth (means ± standard deviations for triplicate cultures) on bromoxynil (18.4 ± 5.2 h) and DBHB (11.9 ± 1.4 h), determined by rate of [14C]lactate uptake into biomass, were similar to those previously reported for this microorganism during growth on pyruvate (15.4 h). In contrast, ioxynil was not deiodinated when added alone or when added with bromoxynil; however, ioxynil dehalogenation, with stoichiometric conversion to 4-cyanophenol, was observed when the culture was amended with 3-chloro-4-hydroxybenzoate (a previously reported electron acceptor). To our knowledge, this is the first direct report of deiodination by a bacterium in the Desulfitobacterium genus and the first report of an anaerobic pure culture with the ability to transform bromoxynil or ioxynil. This research provides valuable insights into the substrate range of D. chlororespirans.

In Situ Generation of Electron Acceptor for Photoelectrochemical Biosensing via Hemin-Mediated Catalytic Reaction

2014 ◽  
Vol 86 (24) ◽  
pp. 12362-12368 ◽  
Author(s):  
Yang Zang ◽  
Jianping Lei ◽  
Lei Zhang ◽  
Huangxian Ju
Keyword(s):  
Electron Acceptor ◽  
Catalytic Reaction ◽  
In Situ Generation

scholarly journals Computational Approach for Ranking Mutant Enzymes According to Catalytic Reaction Rates

2009 ◽  
Vol 113 (11) ◽  
pp. 3579-3583 ◽  
Author(s):  
Malika Kumarasiri ◽  
Gregory A. Baker ◽  
Alexander V. Soudackov ◽  
Sharon Hammes-Schiffer
Keyword(s):  
Catalytic Reaction ◽  
Reaction Rates ◽  
Computational Approach

An algorithm for evaluating reaction rates of catalytic reaction networks with strong diffusion limitations

2001 ◽  
Vol 25 (9-10) ◽  
pp. 1185-1198 ◽  
Author(s):  
Sergio P. Bressa ◽  
Néstor J. Mariani ◽  
Néstor O. Ardiaca ◽  
Germán D. Mazza ◽  
Osvaldo M. Martı́nez ◽  
...  
Keyword(s):  
Catalytic Reaction ◽  
Reaction Rates ◽  
Reaction Networks ◽  
Diffusion Limitations ◽  
Strong Diffusion

Catalytic reaction rates in thermodynamically non-ideal systems

2000 ◽  
Vol 163 (1-2) ◽  
pp. 189-204 ◽  
Author(s):  
Rostam J. Madon ◽  
Enrique Iglesia
Keyword(s):  
Catalytic Reaction ◽  
Reaction Rates

Organic sulfur and organic matter redox processes contribute to electron flow in anoxic incubations of peat

2016 ◽  
Vol 13 (5) ◽  
pp. 816 ◽  
Author(s):  
Zhi-Guo Yu ◽  
Jörg Göttlicher ◽  
Ralph Steininger ◽  
Klaus-Holger Knorr
Keyword(s):  
Carbon Dioxide ◽  
Organic Matter ◽  
Electron Acceptor ◽  
Electron Acceptors ◽  
Organic Sulfur ◽  
Co2 Production ◽  
Bacterial Sulfate Reduction ◽  
Sulfur Species ◽  
Ch4 Production

Environmental contextThe extent to which organic matter decomposition generates carbon dioxide or methane in anaerobic ecosystems is determined by the presence or absence of particular electron acceptors. Evaluating carbon dioxide and methane production in anaerobic incubation of peat, we found that organic matter predominated as an electron acceptor over considered inorganic electron acceptors. We also observed changes in organic sulfur speciation suggesting a contribution of organic sulfur species to the electron-accepting capacity of organic matter. AbstractAn often observed excess of CO2 production over CH4 production in freshwater ecosystems presumably results from a direct or indirect role of organic matter (OM) as electron acceptor, possibly supported by a cycling of oxidised and reduced sulfur species. To confirm the role of OM electron-accepting capacities (EACOM) in anaerobic microbial respiration and to elucidate internal sulfur cycling, peat soil virtually devoid of inorganic electron acceptors was incubated under anaerobic conditions. Thereby, production of CO2 and CH4 at a cumulative ratio of 3.2:1 was observed. From excess CO2 production and assuming a nominal oxidation state of carbon in OM of zero, we calculated a net consumption rate of EACOM of 2.36µmol electron (e–)cm–3day–1. Addition of sulfate (SO42–) increased CO2 and suppressed CH4 production. Moreover, subtracting the EAC provided though SO42–, net consumption rates of EACOM had increased to 3.88–4.85µmol e–cm–3day–1, presumably owing to a re-oxidation of sulfide by OM at sites otherwise not accessible for microbial reduction. As evaluated by sulfur K-edge X-ray absorption near-edge structure spectroscopy, bacterial sulfate reduction presumably involved not only a recycling of inorganic sulfur species, but also a sulfurisation of OM, yielding reduced organic sulfur, and changes in oxidised organic sulfur species. Organic matter thus contributes to anaerobic respiration: (i) directly by EAC of redox-active functional groups; (ii) directly by oxidised organic sulfur; and (iii) indirectly by re-oxidation of sulfide to maintain bacterial sulfate reduction.

Sign in / Sign up

Export Citation Format

Share Document