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1.
The rates of deuterium exchange reactions of malondialdehyde (MDA) and deuterated malondialdehyde (MDAd) have been studied as a function of acidity and the content of dimethyl sulfoxide (DMSO) in binary mixtures with D2O . MDA incorporates deuterium from D2O solutions in a first-order reaction with a rate constant (kobs) that depends on the acid concentration. From this dependence, a catalytic constant, kcat, can be derived (kcatMDA = 2.25 × 105M?s?1). Similar kinetic behavior was found for MDAd in H2O solutions, and in this case, kcatMDA = 1.56 × 105M?1s?1. Results from reactions of MDA and MDAd in identical H2OD2O mixtures show that primary and secondary isotope effects are small (kH/kD = 1.13) and that solvent isotope effects cause most of the differences found between reactions in D2O and H2O. Reactions in binary DMSOd6D2O mixtures show a six-fold rate increase as the proportion of DMSOd6 increases from 50% to 90%. These results also illustrate the relatively high reactivity of MDA at pH values well above its pKa and the importance of medium composition on its reaction rate. 相似文献
2.
The consumption rate of chlorine dioxide in the reaction with the residual lignin was studied using measurements of the potential of a redox couple ClO2/ClO 2 ? in an aqueous suspension of lignocellulose powder material. The methodology was developed for the study of reaction kinetics of chlorine dioxide with the residual lignin using the first order reaction model with the initial lignin concentration in the reaction medium varying in the range of (1–17) × 10–4 М at the initial chlorine dioxide concentration of 4.48 × 10–4 М. The monochronic rate constant of the second order reaction of chlorine dioxide with the residual lignin was calculated by the dependence keff(I) = keff(II)[L]0 under the lignin excess conditions, it was 1462 ± 108 М–1 s–1. Considering the initial concentrations of reagents, it was found that, with increasing the degree of lignin conversion Θ from ≈0.27 to 0.54, its reactivity in the interaction with the chlorine dioxide is reduced, and the value of keff(II) decreased from ≈1280 to 900 М–1 s–1, which according to the theory of polychronic kinetics was a manifestation of the kinetic nonequivalence of the various ensembles of macromolecules of the residual lignin. Thus, it was experimentally shown for the first time that residual lignin of lignocellulose powder material had a kinetic nonequivalence in the interaction with chlorine dioxide. 相似文献
3.
Effect of Residual Lignin Type and Amount on Bleaching of Kraft Pulp by Trametes versicolor 总被引:2,自引:0,他引:2
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The white rot fungus Trametes (Coriolus) versicolor can delignify and brighten unbleached hardwood kraft pulp within a few days, but softwood kraft pulps require longer treatment. To determine the contributions of higher residual lignin contents (kappa numbers) and structural differences in lignins to the recalcitrance of softwood kraft pulps to biobleaching, we tested softwood and hardwood pulps cooked to the same kappa numbers, 26 and 12. A low-lignin-content (overcooked) softwood pulp resisted delignification by T. versicolor, but a high-lignin-content (lightly cooked) hardwood pulp was delignified at the same rate as a normal softwood pulp. Thus, the longer time taken by T. versicolor to brighten softwood kraft pulp than hardwood pulp results from the higher residual lignin content of the softwood pulp; possible differences in the structures of the residual lignins are important only when the lignin becomes highly condensed. Under the conditions used in this study, when an improved fungal inoculum was used, six different softwood pulps were all substantially brightened by T. versicolor. Softwood pulps whose lignin contents were decreased by extended modified continuous cooking or oxygen delignification to kappa numbers as low as 15 were delignified by T. versicolor at the same rate as normal softwood pulp. More intensive O2 delignification, like overcooking, decreased the susceptibility of the residual lignin in the pulps to degradation by T. versicolor. 相似文献
4.
Frank W. Whitmore 《Phytochemistry》1982,21(2):315-318
Cell walls of Pinus elliottii callus contain ca 12 % protein. Klason lignin prepared from the walls contained 9 % protein and represented 4.5 % of the wall. The lignin fraction was increased to 22 % of the wall weight by reacting washed cell-wall tissue with coniferyl alcohol and H2O2, a reaction catalysed by peroxidase that remained bound to the wall. The augmented lignin preparation yielded 10 % protein. The acid hydrolysate of whole wall tissue included five amino acids at a concentration higher than hydroxyproline. The hydrolysates of both natural and augmented lignin preparations yielded distributions of amino acids in which the concentration of hydroxyproline was higher than that of all other amino acids. The results suggest that polymerizing lignin links covalently with cell-wall glycoprotein, and that the bonds may be formed preferentially with hydroxyproline. 相似文献
5.
K. Maharaj M. F. A. Bradfield W. Nicol 《Applied microbiology and biotechnology》2014,98(17):7379-7386
Continuous anaerobic fermentations were performed in a biofilm reactor packed with Poraver® beads. Dilution rates (D) varied between 0.054 and 0.72 h?1, and d-glucose and CO2 gas were used as carbon substrates. Steady-state conditions were shown to be repeatable and independent of the operational history. Production stability was achieved over periods exceeding 80 h at values of D below 0.32 h?1. In these situations, steady-state variation (expressed as fluctuations in NaOH neutralisation flow rates) exhibited a standard deviation of less than 5 % while no indication of biofilm deactivation was detected. The total biomass amount was found to be independent of the dilution rate with an average dry concentration of 23.8?±?2.9 g L?1 obtained for all runs. This suggests that the attachment area controls the extent of biofilm accumulation. Specific succinic acid (SA) productivities, based on the total biomass amount, exhibited a substantial decrease with decreasing D. An SA volumetric productivity of 10.8 g L?1 h?1 was obtained at D?=?0.7 h?1—the highest value reported to date in Actinobacillus succinogenes fermentations. SA yields on glucose increased with decreasing D, with a yield of 0.90?±?0.01 g g?1 obtained at a D of 0.054 h?1. Production of formic acid approached zero with decreasing D, while the succinic to acetic acid ratio increased with decreasing D, resulting in an increasing SA yield on glucose. 相似文献
6.
Ian M. Morrison 《Phytochemistry》1975,14(2):505-508
The rates of delignification of samples of Lolium perenne at four different stages of maturity and a sample of Trifolium pratense by the action of sodium chlorite-acetic acid have been determined. For samples with lignin contents of < 8%, delignification was essentially complete within 30 min. The yield and composition of hemicelluloses obtained by alkaline extraction of cell walls was dependent on the duration of the delignification reaction. 相似文献
7.
The effect of different treatments on the enzymatic hydrolysis of furfural residue (FR) was investigated in delignification and structural features. In this case, hot water, ethanol, sodium hydroxide, alkali ethanol, and alkaline hydrogen peroxide solution (AHP) were selected as the delignification solvents. The structure and morphology of the original and treated samples were comparatively studied by diffuse reflectance infrared Fourier transform spectrometry (DRIFT), XRD, SEM, and CP/MAS 13C NMR. After AHP treatment, the ratio of total lignin to cellulose content in FR and the absorbance ratio of lignin to cellulose (A 1508/A 1057) on the sample surface in the DRIFT spectra was reduced from 0.99 to 0.13 and from 0.40 to 0.04, respectively, which resulted in the highest conversion of cellulose to glucose (99.3 %). It was found that the crystallinity index of FR linearly increased with the decrease of total lignin to cellulose ratio. DRIFT analysis indicated that the high lignin content on the sample surface resulted in a low enzymatic hydrolysis efficiency. 相似文献
8.
The white rot basidiomycete Trametes (Coriolus) versicolor can substantially increase the brightness and decrease the lignin content of washed, unbleached hardwood kraft pulp (HWKP). Monokaryotic strain 52J was used to study how HWKP and the lignin in HWKP affect the carbon metabolism and secretions of T. versicolor. Earlier work indicated that a biobleaching culture supernatant contained all components necessary for HWKP biobleaching and delignification, but the supernatant needed frequent contact with the fungus to maintain these activities. Thus, labile small fungal metabolites may be the vital biobleaching system components renewed or replaced by the fungus. Nearly all of the CO2 evolved by HWKP-containing cultures came from the added glucose, indicating that HWKP is not an important source of carbon or energy during biobleaching. Carbon dioxide appeared somewhat earlier in the absence of HWKP, but the culture partial O2 pressure was little affected by the presence of pulp. The presence of HWKP in a culture markedly increased the culture's production of a number of acidic metabolites, including 2-phenyllactate, oxalate, adipate, glyoxylate, fumarate, mandelate, and glycolate. Although the total concentration of these pulp-induced metabolites was only 4.3 mM, these compounds functioned as effective manganese-complexing agents for the manganese peroxidase-mediated oxidation of phenol red, propelling the reaction at 2.4 times the rate of 50 mM sodium malonate, the standard chelator-buffer. The presence of HWKP in a culture also markedly stimulated fungal secretion of the enzymes manganese peroxidase, cellulase, and cellobiose-quinone oxidoreductase, but not laccase (phenol oxidase) or lignin peroxidase. 相似文献
9.
Richard B.M. Schasfoort Kiki C. Andree Niels van der Velde Alex van der Kooi Ivan Stojanović Leon W.M.M. Terstappen 《Analytical biochemistry》2016
The values of the affinity constants (kd, ka, and KD) that are determined by label-free interaction analysis methods are affected by the ligand density. This article outlines a surface plasmon resonance (SPR) imaging method that yields high-throughput globally fitted affinity ranking values using a 96-plex array. A kinetic titration experiment without a regeneration step has been applied for various coupled antibodies binding to a single antigen. Globally fitted rate (kd and ka) and dissociation equilibrium (KD) constants for various ligand densities and analyte concentrations are exponentially interpolated to the KD at Rmax = 100 RU response level (KDR100). 相似文献
10.
Characterization of Palo Podrido, a Natural Process of Delignification in Wood 总被引:4,自引:0,他引:4
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Eduardo Agosin Robert A. Blanchette Herman Silva Catherine Lapierre Kory R. Cease Rebecca E. Ibach Andr R. Abad Pedro Muga 《Applied microbiology》1990,56(1):65-74
Chemical and morphological changes of incipient to advanced stages of palo podrido, an extensively delignified wood, and other types of white rot decay found in the temperate forests of southern Chile were investigated. Palo podrido is a general term for white rot decay that is either selective or nonselective for the removal of lignin, whereas palo blanco describes the white decayed wood that has advanced stages of delignification. Selective delignification occurs mainly in trunks of Eucryphia cordifolia and Nothofagus dombeyi, which have the lowest lignin content and whose lignins have the largest amount of β-aryl ether bonds and the highest syringyl/guaiacyl ratio of all the native woods included in this study. A Ganoderma species was the main white rot fungus associated with the decay. The structural changes in lignin during the white rot degradation were examined by thioacidolysis, which revealed that the β-aryl ether-linked syringyl units were more specifically degraded than the guaiacyl ones, particularly in the case of selective delignification. Ultrastructural studies showed that the delignification process was diffuse throughout the cell wall. Lignin was first removed from the secondary wall nearest the lumen and then throughout the secondary wall toward the middle lamella. The middle lamella and cell corners were the last areas to be degraded. Black manganese deposits were found in some, but not all, selectively delignified samples. In advanced stages of delignification, almost pure cellulose could be found, although with a reduced degree of polymerization. Cellulolytic enzymes appeared to be responsible for depolymerization. A high brightness and an easy refining capacity were found in an unbleached pulp made from selectively delignified N. dombeyi wood. Its low viscosity, however, resulted in poor resistance properties of the pulp. The last stage of degradation (i.e., decomposition of cellulose-rich secondary wall layers) resulted in a gelatinlike substance. Ultrastructural and chemical analyses of this substance showed the matrix to have no microfibrillar structure characteristic of woody cell walls but to still be rich in glucan. 相似文献
11.
Biological Delignification of Aspen Wood by Solid-State Fermentation with the White-Rot Fungus Merulius tremellosus 总被引:4,自引:4,他引:0
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Ian D. Reid 《Applied microbiology》1985,50(1):133-139
Solid-state fermentation of aspen (Populus tremuloides) wood with Merulius tremellosus for 8 weeks removed 52% of the lignin but only 12% of the total wood weight, and increased the cellulase digestibility to 53% from 18%. Water-soluble and enzyme-solubilized lignin degradation products accumulated. Delignification was fastest at temperatures between 25 and 32.5°C and at a water-to-wood ratio of 2. Initial pH values between 4 and 6 were optimal; M. tremellosus acidified the wood to below pH 3.5 as it grew. The fungus tolerated CO2 concentrations of at least 14% and O2 concentrations down to 7% in the bulk gas phase. Both simple and complex nitrogen supplements inhibited delignification. Supplementary KH2PO4, MgSO4, CaCl2, thiamine, and trace elements had little effect on the fermentation. Four isolates of M. tremellosus had very similar abilities to delignify aspen wood. Biological delignification with M. tremellosus may be a useful pretreatment for enzymatic saccharification or ruminant feeding. 相似文献
12.
Lignin Peroxidase Activity Is Not Important in Biological Bleaching and Delignification of Unbleached Kraft Pulp by Trametes versicolor 总被引:9,自引:8,他引:1
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Frederick S. Archibald 《Applied microbiology》1992,58(9):3101-3109
The discovery in 1983 of fungal lignin peroxidases able to catalyze the oxidation of nonphenolic aromatic lignin model compounds and release some CO2 from lignin has been seen as a major advance in understanding how fungi degrade lignin. Recently, the fungus Trametes versicolor was shown to be capable of substantial decolorization and delignification of unbleached industrial kraft pulps over 2 to 5 days. The role, if any, of lignin peroxidase in this biobleaching was therefore examined. Several different assays indicated that T. versicolor can produce and secrete peroxidase proteins, but only under certain culture conditions. However, work employing a new lignin peroxidase inhibitor (metavanadate ions) and a new lignin peroxidase assay using the dye azure B indicated that secreted lignin peroxidases do not play a role in the T. versicolor pulp-bleaching system. Oxidative activity capable of degrading 2-keto-4-methiolbutyric acid (KMB) appeared unique to ligninolytic fungi and always accompanied pulp biobleaching. 相似文献
13.
14.
In O2 equilibrium studies of hemoglobin it was observed that the presence of urea increases f502 and decreases co-operativity. The results were interpreted on the basis of unfolding and swelling of the peptide chains. The results of the present kinetic investigation indicate that while the CO combination rate constants for αSH chains, hemoglobin H and myoglobin do not change with increasing concentrations of urea, the corresponding rate constants for deoxy hemoglobin A increase continuously with urea concentration. At urea concentrations of 4 m or more, the reaction time course becomes biphasic. The fast component of the reaction time course yields CO combination rate constants which are in close agreement with the rate constants of dimeric and monomeric hemoglobins. These results indicate that up to 4 m-urea the kinetic and equilibria parameters increase due to weakened constraints imposed by intersubunit contacts and bonds. At higher urea concentrations Hb4 is significantly dissociated into dimers and monomers, and hence the high ligand affinity and decreased co-operativity of the system. The implications of higher ligand combination rate constants of the deoxyhemoglobin tetramer in the presence of urea on the reaction mechanism are discussed. 相似文献
15.
The ability of 12 Cyathus species to degrade 14C-labeled lignin in kenaf was studied. The sum of 14C released into solution plus 14C released into the gas phase over a 32-day fermentation period was used to determine average daily rates of lignin biodegradation. Cyathus pallidus. C. africanus, and C. berkeleyanus delignified kenaf most rapidly. C. canna showed the greatest preference for lignin degradation over other plant components, and its rate of lignin degradation was only slightly lower than the three most active species. The apparent ability of fungi to metabolize low-molecular-weight lignin breakdown products correlated well with their overall delignification rates. C. stercoreus metabolized degradation products of lignin from wheat straw better than those from kenaf lignin, based on the amount of low-molecular-weight products left in solution. 相似文献
16.
M. A. Rosenfeld A. N. Shchegolikhin A. V. Bychkova V. B. Leonova M. I. Biryukova E. A. Kostanova M. L. Konstantinova 《Biochemistry. Biokhimii?a》2013,78(10):1171-1179
Ozone-induced oxidation of fibrinogen has been investigated. The conversion of oxidized fibrinogen to fibrin catalyzed either by thrombin or by a reptilase-like enzyme, ancistron, in both cases is accompanied by production of gels characterized by a higher weight/length ratio of fibrils in comparison with the native fibrin gels. IR spectra of the D and E fragments isolated from unoxidized and oxidized fibrinogen suggest a noticeable transformation of functional groups by oxidation. A decrease in content of N-H groups in the peptide backbone and in the number of C-H bonds in aromatic structures, as well as a decrease in the intensity of the C-H valence vibrations in aliphatic fragments CH2 and CH3 were found. The appearance in the differential spectra of the D fragments of rather intense peaks in the interval of 1200–800 cm?1 clearly indicates the interaction of ozone with amino acid residues of methionine, tryptophan, histidine, and phenylalanine. Comparison of the differential spectra for the D and E fragments suggests that fibrinogen fragment D is more sensitive to the oxidant action than fragment E. Using EPR spectroscopy, differences are found in the spectra of spin labels bound with degradation products of oxidized and unoxidized fibrinogen, the D and E fragments, caused by structural and dynamical modifications of the protein molecules in the areas of localization of the spin labels. The relationship between the molecular mechanism of oxidation of fibrinogen and its three-dimensional structure is discussed. 相似文献
17.
A successful method for the purification of NADP isocitrate dehydrogenase from a plant source, Zea mays, is reported. Two mitochondrial isoenzymes were found and purified to homogeneity by a course of acetone fractionation, bulk exchange on DEAE-cellulose, cellulose hydroxylapatite column chromatography, and continuous elution electrophoresis. The mitochondrial isoenzymes are very similar with respect to kinetic properties, response to solvent perturbation, and temperature dependence of the pH/V relationship of isocitrate dehydrogenation. The Michaelis constant for isocitrate is identical for both isoenzymes. The enzymes have a molecular weight of 81,000 as estimated by permeation chromatography and an isoelectric point of 5.5 as extrapolated from gel-electrophoretic mobilities. Detectable differences are confined to differences in electrophoretic mobilities and heat denaturation. In D2O the rate of the overall reaction from isocitrate to α-ketoglutarate and CO2 was about 3.6 times slower than the same reaction in H2O. Both the forward and reverse reactions, in which isocitrate is dehydrogenated or generated from oxalosuccinate, were observed to decrease by this amount in D2O. The decarboxylation of oxalosuccinate was found to decrease by only about 25% in D2O relative to the velocity of the reaction in H2O. Thus the slow step in the overall reaction must be the initial dehydrogenation step rather than the decarboxylation of oxalosuccinate. The pK of the overall reaction did not change in D2O as compared to H2O. 相似文献
18.
Eucalyptus globulus wood fractionation by autohydrolysis and organosolv delignification 总被引:1,自引:0,他引:1
This work provides an assessment on the fractionation of Eucalyptus globulus wood by sequential stages of autohydrolysis (to cause the solubilization of hemicelluloses) and organosolv pulping (to dissolve lignin, leaving solids enriched in cellulose). With this approach, valuable products (hemicellulose-derived saccharides, sulphur-free lignin fragments and cellulosic substrates with low contents of residual hemicelluloses) are obtained in separate streams, according to the biomass refinery approach. Autohydrolysis was carried out under optimized operational conditions, and organosolv pulping was performed using uncatalyzed ethanol-water solutions. The effects of the most influential operational variables (autohydrolysis severity, delignification temperature and ethanol concentration in the organosolv stage) on solid yield, solid composition, cellulose susceptibility and recovery of the various fractions was assessed using statistical methods, which enabled the identification of the most favourable operational conditions. 相似文献
19.
Youping Zhou Hilary Stuart-Williams Graham D. Farquhar Charles H. Hocart 《Phytochemistry》2010,71(8-9):982-993
Qualitative and quantitative understanding of the chemical linkages between the three major biochemical components (cellulose, hemicellulose and lignin) of plant cell walls is crucial to the understanding of cell wall structure. Although there is convincing evidence for chemical bonds between hemicellulose and lignin and the absence of chemical bonds between hemicellulose and cellulose, there is no conclusive evidence for the presence of covalent bonds between cellulose and lignin. This is caused by the lack of selectivity of current GC/MS-, NMR- and IR-based methods for lignin characterisation as none of these techniques directly targets the possible ester and ether linkages between lignin and cellulose. We modified the widely-accepted “standard” three-step extraction method for isolating cellulose from plants by changing the order of the steps for hemicellulose and lignin removal (solubilisation with concentrated NaOH and oxidation with acetic acid-containing NaClO2, respectively) so that cellulose and lignin could be isolated with the possible chemical bonds between them intact. These linkages were then cleaved with NaClO2 reagent in aqueous media of contrasting 18O/16O ratios. We produced cellulose with higher purity (a lower level of residual hemicellulose and no detectable lignin) than that produced by the “standard” method. Oxidative artefacts may potentially be introduced at the lignin removal stage; but testing showed this to be minimal.Cellulose samples isolated from processing plant-derived cellulose–lignin mixtures in media of contrasting 18O/16O ratios were compared to provide the first quantitative evidence for the presence of oxygen-containing ester and ether bonds between cellulose and lignin in Zea mays leaves. However, no conclusive evidence for the presence or lack of similar bonds in Araucaria cunninghamii wood was obtained. 相似文献
20.
A widespread and hitherto by far underexploited potential among ecologically diverse fungi to pretreat wheat straw and digestate from maize silage in the future perspective of using such lignocellulosic feedstock for fermentative bioenergy production was inferred from a screening of nine freshwater ascomycetes, 76 isolates from constructed wetlands, nine peatland isolates and ten basidiomycetes. Wheat straw pretreatment was most efficient with three ascomycetes belonging to the genera Acephala (peatland isolate) and Stachybotrys (constructed wetland isolates) and two white-rot fungi (Hypholoma fasciculare and Stropharia rugosoannulata) as it increased the amounts of water-extractable total sugars by more than 50 % and sometimes up to 150 % above the untreated control. The ascomycetes delignified wheat straw at rates (lignin losses between about 31 and 40 % of the initial content) coming close to those observed with white-rot fungi (about 40 to 57 % lignin removal). Overall, fungal delignification was indicated as a major process facilitating the digestibility of wheat straw. Digestate was generally more resistant to fungal decomposition than wheat straw. Nevertheless, certain ascomycetes delignified this substrate to extents sometimes even exceeding delignification by basidiomycetes. Total sugar amounts of about 20 to 60 % above the control value were obtained with the most efficient fungi (one ascomycete of the genus Phoma, the unspecific wood-rot basidiomycete Agrocybe aegerita and one unidentified constructed wetland isolate). This was accompanied by lignin losses of about 47 to 56 % of the initial content. Overall, digestate delignification was implied to be less decisive for high yields of fermentable sugars than wheat straw delignification. 相似文献