Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “LIGNIN”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 253 records · Page 14Linked to original sources
PubMed2005

Lignin primary structures and dirigent sites.

Although lignin is the second most abundant plant substance in vascular plants, its mode of synthesis is still the subject of much debate. However, recent progress has provided crucial evidence to support the theory that lignin primary structure is controlled at the proteinaceous level. Evidence for control over lignin assembly has been demonstrated with the discovery of monomer-invariant aryl-O-ether linkages in lignins that upon alkaline cleavage release the corresponding monomers in equimolar amounts, regardless of monolignol composition. Current evidence would indicate that there are only a few native lignin primary structures, the entire sequences of which now need to be fully determined. A provisional mechanistic model is proposed to account for macromolecular lignin assembly through the participation of proteins harboring arrays of dirigent (monolignol radical binding) sites.

Binding Sites↗
PubMedDate not supplied

Towards a new concept of lignin condensation in kraft pulping. Initial results.

In kraft pulping, a comparatively large amount of lignin remains in the fibres after the cook. Based on various analytical techniques for lignin, such as thioacidolysis, GPC and NMR, it is suggested that lignin condensation reactions take place during the cook. The reaction seems, however, not to involve ionic intermediates as has been suggested previously but rather a one-electron mechanism with elemental sulphur as the initiator. Support for such a reaction has been found through kraft cooks in the presence of an added phenol, 2,6-xylenol, as well as through NMR analysis of kraft lignin. It was found that the added phenol is incorporated in the pulp lignin with linkages indicative of radical coupling. Furthermore, kraft lignin was found to contain substantial amounts of chemically linked fatty acids. By complementary analyses of sulphur and polysulphide in an industrial black liquor, the presence of these compounds throughout a kraft cook was demonstrated.

Chromatography, Gel↗
PubMed2004

Signatures of cinnamyl alcohol dehydrogenase deficiency in poplar lignins.

A series of transgenic poplars down-regulated for cinnamyl alcohol dehydrogenase (CAD) was analyzed by thioacidolysis. Among the lignin-derived monomers, the indene compounds that were recently shown to originate from sinapaldehyde incorporated into lignins through 8-O-4-cross-coupling, were found to increase as a function of CAD deficiency level. While these syringyl markers were recovered in substantial amounts in the most severely depressed lines, the markers for coniferaldehyde incorporation were recovered in only low amounts. In conjunction with these additional sinapaldehyde units and relative to the control samples, lignins in CAD-deficient poplar lines had less conventional syringyl-units and beta-O-4-bonds and more free phenolic groups. We found that almost half of the polymers in the most deficient lines could be solubilized in alkali and at room temperature. This unusual behavior suggests that lignins in CAD-deficient poplars occur as small, alkali-leachable lignin domains. That mainly sinapaldehyde incorporates into the lignins of CAD-deficient poplars suggests that the recently identified sinapyl alcohol dehydrogenase (SAD), which is structurally distinct from the CAD enzyme targeted herein, does not play any substantial role in constitutive lignification in poplar.

Acrolein↗
PubMed2004

O-Methylation of benzaldehyde derivatives by "lignin specific" caffeic acid 3-O-methyltransferase.

Although S-adenosyl-l-methionine (SAM) dependent caffeic acid/5-hydroxyferulic acid 3/5-O-methyltransferase (COMT) is one of the key enzymes in lignin biosynthesis, the present work demonstrates that alfalfa COMT methylates benzaldehyde derivatives more efficiently than lignin pathway intermediates. 3,4-Dihydroxy, 5-methoxybenzaldehyde and protocatechuic aldehyde were the best in vitro substrates for OMT activity in extracts from developing alfalfa stems, and these compounds were preferred over lignin pathway intermediates for 3-O-methylation by recombinant alfalfa COMT expressed in Escherichia coli. OMT activity with benzaldehydes was strongly reduced in extracts from stems of transgenic alfalfa down-regulated in COMT. However, although COMT down-regulation drastically affects lignin composition, it does not appear to significantly impact metabolism of benzaldehyde derivatives in alfalfa. Structurally designed site-directed mutants of COMT showed altered relative substrate preferences for lignin precursors and benzaldehyde derivatives. Taken together, these results indicate that COMT may have more than one role in phenylpropanoid metabolism (but probably not in alfalfa), and that engineered COMT enzymes could be useful for metabolic engineering of both lignin and benzaldehyde-derived flavors and fragrances.

Amino Acid Substitution↗
PubMed2026

GA4+7 alleviates pear fruit semi-russeting partly by suppressing PRX-mediated lignin deposition.

Pear fruit semi-russeting is a surface disorder that frequently occurs during fruit development and significantly diminishes fruit appearance quality and commercial value. Although Gibberellin 4 + 7 (GA4+7) has been used to reduce fruit surface defects in horticultural crops, the physiological and molecular mechanisms underlying its inhibitory effect on pear fruit semi-russeting remain poorly understood. In this study, preharvest GA4+7 treatment of 'Cuiguan' pear significantly reduced russet coverage and lignin accumulation in mature fruit skin without adversely affecting fruit size, fruit shape index, or total soluble solids content. Integrated metabolomic and transcriptomic analyses revealed that GA4+7 treatment was associated with the repression of phenylpropanoid and lignin biosynthesis at both metabolic and transcriptional levels. Among the lignin-related differentially expressed genes, two class III peroxidase genes, PpyPRX22 and PpyPRX65, were strongly downregulated by both GA4+7 and bagging treatments. Both proteins localized to the cell wall, and transient expression assays in pear fruit skin supported positive roles for PpyPRX22 and PpyPRX65 in lignin deposition. Furthermore, dual-luciferase reporter assays combined with transient overexpression experiments suggested that several PpyMYB transcription factors may regulate PpyPRX expression and lignin accumulation, with PpyMYB138 and PpyMYB139 significantly activating PpyPRX22 and/or PpyPRX65 promoter activity. Taken together, these results suggest that GA4+7 alleviates pear fruit semi-russeting at least partly by reducing lignin deposition in the fruit skin, with PpyPRX22 and PpyPRX65 potentially contributing to this process.

Class III peroxidase↗
PubMed1975

Presence of soluble lignin-carbohydrate complexes in the bovine rumen.

The cell-free rumen liquor of a steer on a diet of spear grass has been shown to contain macromolecular substances in which carbohydrates and lignin-derived compounds are covalently bound to each other. The lignin-carbohydrate complexes are soluble at pH 7 or higher, but precipitate at pH 3. At the latter pH, small amounts of a polymer, assumed to be glycoprotein, remain in solution. Some of the lignin-carbohydrate linkages are broken by treatment with alkali. Treatment with 50mM sulphuric acid for a few minutes at room temperature converts part of the complex into an acetone-soluble product, which still contains both carbohydrate and lignin-derived compounds. The formation of soluble lignin-carbohydrate complexes by the action of rumen micro-organisms on the grass may account for the dissolution (and hence the apparent digestion) of about half of the total lignin-intake.

Acetone↗
PubMed2000

Do the extracellular enzymes cellobiose dehydrogenase and manganese peroxidase form a pathway in lignin biodegradation?

The extracellular enzyme manganese peroxidase is believed to degrade lignin by a hydrogen peroxide-dependent oxidation of Mn(II) to the reactive species Mn(III) that attacks the lignin. However, Mn(III) is not able to directly oxidise the non-phenolic lignin structures that predominate in native lignin. We show here that pretreatment of a non-phenolic lignin model compound with another extracellular fungal enzyme, cellobiose dehydrogenase, allows the manganese peroxidase system to oxidise this molecule. The mechanism behind this effect is demethoxylation and/or hydroxylation, i.e. conversion of a non-phenolic structure to a phenolic one, mediated by hydroxyl radicals generated by cellobiose dehydrogenase. This suggests that cellobiose dehydrogenase and manganese peroxidase may act in an extracellular pathway in fungal lignin biodegradation. Analytical techniques used in this paper are reverse-phase high-pressure liquid chromatography, gas chromatography connected to mass spectroscopy and UV-visible spectroscopy.

Anisoles↗
PubMed2001

The phenolic fraction of maize bran: evidence for lignin-heteroxylan association.

Maize bran heteroxylan samples were extracted in various conditions of severity. Their ferulate and diferulate content was investigated by GC-MS of methyl ester-TMSi derivatives. When extracted by 0.5 M NaOH in mild conditions, the heteroxylan sample contained a low level of ferulic acid (0.032% by wt.) and the main diferulate surviving alkaline extraction was found to be the 8-8' diferulate. On peroxidase treatment, this sample nevertheless produced a firm and brittle gel without any change in the diferulate profile. Typical lignin structures, mainly comprising syringyl units interconnected through beta-O-4, beta-1 and beta-beta interunit bonds, were evidenced in the maize bran sample. More importantly, these lignin structures were found to be tightly associated with the alkali-extracted heteroxylans. Thioacidolysis revealed the occurrence of 0.1-0.5% (by wt.) lignin structures in heteroxylan fractions extracted in mild or severe conditions, before and after purification of the polysaccharides. The gelling potential of the heteroxylan fractions was not only dependent on their ferulate level, but also influenced by associated lignin structures. These results argue for the occurrence of covalent linkages between heteroxylan chains and lignin structures which could participate in the peroxidase-driven gelation of feruloylated polysaccharides. They demonstrate the role of low lignin levels in the organization of native or reconstructed polysaccharide networks.

Chromatography, High Pressure Liquid↗
PubMed1998

Copper-dependent depolymerization of lignin in the presence of fungal metabolite, pyridine.

Thus far, it has not been recognized that copper complexes are able to depolymerize lignin under physiological conditions of white rot decay. However, we have found that both phenolic and non-phenolic synthetic lignins were intensively depolymerized by Cu(II) and lipid hydroperoxide model compounds in the presence of a metabolite of ligninolytic fungi, pyridine at room temperature in aqueous media. Treatment of 14C-labeled oxygen-prebleached kraft pulp (OKP) by the copper-dependent reaction evidenced effectiveness of this reaction for the delignification of kraft pulps. In contrast to the organic peroxide system, Cu(II)/pyr/H2O2 system was much less effective for the lignin depolymerization. However, treatment of unbleached kraft pulp (UKP) by Cu(II)/H2O2 and Cu(II)/pyr/H2O2 systems demonstrated that the damage of cellulose was suppressed by the coordination of pyridine although high brightness gain was obtained independently of the presence of the coordinator. Spin trapping experiments demonstrated that not hydroxyl radical but superoxide anion is involved in the Cu(II)/pyr/H2O2 system. This finding not only introduces a new concept of non-enzymatic lignin biodegradation by wood-degrading fungi but also presents a new strategy for decomposing lignin and lignin-related compounds by copper complexes and peroxide-producing system.

Biopolymers↗
PubMed2002

Determination of the carbonyl groups in native lignin utilizing Fourier transform Raman spectroscopy.

A near-infrared Fourier transform Raman (NIR-FTR) spectroscopic technique was utilized to determine the chemical structure of lignin in a woody matrix. In the NIR-FTR spectra of coniferaldehyde and coniferyl alcohol, the Raman bands for the carbonyl group and the alpha, beta unsaturated bond were detected at 1620 and 1660 cm(-1), respectively. These peaks were also found in the NIR-FTR spectra of chemically synthesized lignins, isolated lignin from conifer wood, and conifer wood meal. Upon the reduction of carbonyl groups in the lignin samples and wood meal, the band at 1620 cm(-1) disappeared; on the other hand, the band at 1660 cm(-1) remained unchanged. However, upon the oxidation of reduced lignin at the benzyl hydroxyl group using dicyanodichrolobenzoquinone, the band at 1620 cm(-1) clearly appeared, strongly suggesting that the band at 1620 cm(-1) can be assigned as a carbonyl marker band. The hydrogenation reaction optimized for the reduction of the unsaturated bond in lignin caused the disappearance of the band at 1660 cm(-1), indicating that the band at 1660 cm(-1) is an alpha, beta unsaturated bond marker band. The change in carbonyl content during the wood decay process was also shown to be monitored using the Raman intensity of the carbonyl marker band. It was indicated that the NIR-FTR spectroscopic techniques were suitable analytical method for a rapid and nondestructive analysis of wood samples.

Cedrus↗
PubMed2000

Isolation and quantification of dissolved lignin from natural waters using solid-phase extraction and GC/MS.

Solid-phase extraction (SPE) was tested for the isolation of dissolved lignin from diverse natural waters (fresh, estuarine, and marine) in preparation for CuO oxidation. Capillary GC coupled to selected-ion monitoring mass spectrometry (SIM-MS) of CuO oxidation products provides the high sensitivity and precision required for the identification and quantification of trace levels of lignin in seawater. The low blanks and quick cleanup of C18 cartridges support SPE for processing such samples. Comparison of SPE with other isolation procedures (direct dry-down and ultrafiltration) has shown that this method quantitatively recovers dissolved lignin and preserves its compositional parameters. The concentration and nature of dissolved organic matter appear to be primary factors that constrain the amount of water that should be processed to obtain quantitative and reproducible recoveries of dissolved lignin using SPE. Highest recoveries of dissolved lignin were obtained at low pH (1.5-4.0) with substantial decreases at pH > 4. Extraction efficiencies were independent of flow rate within a range of five to fifteen bed volumes per minute (50-150 mL min(-1)), and both refrigeration and freezing were appropriate long-term storage methods for processed cartridges prior to elution of retained dissolved lignin.

Gas Chromatography-Mass Spectrometry↗
PubMedDate not supplied

Structural differences between the lignin-carbohydrate complexes present in wood and in chemical pulps.

Lignin-carbohydrate complexes (LCCs) were prepared in quantitative yield from spruce wood and from the corresponding kraft and oxygen-delignified pulps and were separated into different fractions on the basis of their carbohydrate composition. To obtain an understanding of the differences in lignin structure and reactivity within the various LCC fractions, thioacidolysis in combination with gas chromatography was used to quantify the content of beta-O-4 structures in the lignin. Periodate oxidation followed by determination of methanol was used to quantify the phenolic hydroxyl groups. Furthermore, size exclusion chromatography (SEC) of the thioacidolysis fractions was used to monitor any differences between the original molecular size distribution and that after the delignification processes. Characteristic differences between the various LCC fractions were observed, clearly indicating that two different forms of lignin are present in the wood fiber wall. These forms are linked to glucomannan and xylan, respectively. On pulping, the different LCCs have different reactivities. The xylan-linked lignin is to a large extent degraded, whereas the glucomannan-linked lignin undergoes a partial condensation to form more high molecular mass material. The latter seems to be rather unchanged during a subsequent oxygen-delignification stage. On the basis of these findings, a modified arrangement of the fiber wall polymers is suggested.

Acetone↗
PubMedDate not supplied

Down-regulation of lignin biosynthesis in transgenic Leucaena leucocephala harboring O-methyltransferase gene.

In the present study, a 0.47 kb OMT gene construct from aspen, encoding for an enzyme O-methyltransferase (OMT, EC 2.1.1.6), in antisense orientation was used to down-regulate lignin biosynthesis in Leucaena leucocephala. The plants were transformed with Agrobacterium tumefaciens strain harboring the antisense gene, and the transformation was confirmed by PCR amplification of the npt II gene. The integration of a heterologous antisense OMT gene construct in transformed plants led to a maximum of 60% reduction in OMT activity relative to control. The evaluation of total lignin content by the Klason method revealed a maximum of 28% reduction. Histochemical analyses of stem sections depicted a reduction in lignin content and normal xylem development. The results also suggested a probable increase in aldehyde levels and a decrease in syringyl units. Lignin down-regulation was accompanied by an increase in methanol soluble phenolics to an extent that had no impact on wood discoloration, and the plants displayed a normal phenotype. Concomitantly, an increase of up to 9% in cellulose content was also observed. Upon alkali extraction, modified lignin was more extractable as evident from reduced Klason lignin in saponified residue and increased alkali soluble phenolics. The results together suggested that the extent of down-regulation of OMT activity achieved may lead to quality amelioration of Leucaena with respect to its applicability in pulp and paper manufacture as well as nutritive and easily digestible forage production.

Down-Regulation↗
PubMed2000

Controlled release of a herbicide from matrix granules based on solvent-fractionated organosolv lignins.

An organosolv (Alcell) lignin was fractionated with both sequential solvent-extraction and solvent-mixture precipitation using various organic solvent systems. The resulting fractionated lignins were used to prepare matrix granules with bromacil as a model compound using a melt process. The release rates of bromacil in vitro from the granular matrix system were influenced by both the lignin used as carrier and the solution fractionation. The variations in release rates were related to the high proportion of low-molecular-weight fraction and its associated water-soluble lignin in the fractionated lignins. Fickian diffusion was a predominant factor in controlling the release of bromacil from the matrix granules based on the low-molecular-weight fraction (L(fr1)). For the matrix granules based on the other fractionated lignins, the release of bromacil was of super-case II transport. The fine structure of the matrix granules before and after release was also studied. An unique release pattern of bromacil was observed for the matrix granules based on the low-molecular-weight fraction (L(fr1)), showing a fast release followed by zero-order release, which was a result of remarkable changes in the structure of the matrix granules during the course of release.

Herbicides↗
PubMed2001

Comprehensive study on the chemical structure of dioxane lignin from plantation Eucalyptus globulus wood.

Results of a comprehensive study on the chemical structure of lignin from plantation Eucalyptus globulus Labill are presented. Lignin has been isolated by a modified mild acidolysis method and thoroughly characterized by functional group analysis, by a series of degradation techniques (nitrobenzene oxidation, permanganate oxidation, thioacidolysis, and Py-GC-MS), and (1)H and (13)C NMR spectroscopy. Plantation Eucalyptus globulus lignin was found to be of the S/G type with an extremely high proportion of syringyl (S) units (82-86%) and a minor proportion of p-hydrophenyl propane (H) units (roughly 2-3 mol %). Unknown C-6 substituted and 4-O-5' type syringyl substructures represent about 65% of lignin "condensed" structures. Eucalypt lignin showed high abundance of beta-O-4 (0.56/C(6)) structures and units linked by alpha-O-4 bonds (0.23/C(6)). The proportion of phenylcoumaran structures was relatively low (0.03/C(6)). Different kinds of beta-beta substructures (pino-/syringaresinol and isotaxiresinol types) in a total amount of 0.13/C(6) were detected. ESI-MS analysis revealed a wide molecular weight distribution of lignin with the center of gravity of mass distribution around 2500 u.

Dioxanes↗
PubMed2001

Quantitative (13)C NMR analysis of lignins with internal standards.

Novel protocols for acquiring quantitative (13)C NMR spectra of lignins have been developed using the internal reference compounds 1,3,5-trioxane and pentafluorobenzene. Trioxane offers a convenient internal standard for collecting inverse gated proton decoupled (13)C NMR spectra for lignins, whereas pentafluorobenzene can be used to provide information on the amount of methine carbon using the DEPT experiment. In each case, the internal reference compounds provide single, un-overlapped sharp signals in the middle of the spectral region, permitting facile integration. These integrals could be used to determine the amounts of different structural features of lignins, expressed in absolute units of millimoles per gram. The optimum parameters for these experiments were validated for a variety of spectrometer platforms, and standard errors were determined for different spectral areas using lignin model compounds and "standard" lignins. In addition, the data derived for the International Round Robin "standard" lignins showed good agreement with the data from quantitative (31)P NMR spectroscopy and published data, obtained by independent laboratories using independent methods of analysis.

Carbon Isotopes↗
PubMed2002

Abundance and reactivity of dibenzodioxocins in softwood lignin.

To define the abundance and comprehend the reactivity of dibenzodioxocins in lignin, model compound studies, specific degradation experiments on milled wood lignin, and molecular modeling calculations have been performed. Quantitative (31)P NMR measurements of the increase of biphenolic hydroxyl groups formed after a series of alkaline degradations in the presence of hydrosulfide anions (kraft conditions) showed the presence of 3.7 dibenzodioxocin rings/100 C9 units in milled wood lignin. The DFRC degradation protocol (Derivatization Followed by Reductive Cleavage) was chosen as an independent means to estimate their abundance. Initial experiments with a dibenzodioxocin model compound, trans-6,7-dihydro-7-(4-hydroxy-3-methoxyphenyl)-4,9-dimethoxy-2,11-dipropyldibenzo[e,g][1,4]dioxocin-6-ylmethanol, showed that it is not cleaved under DFRC conditions, but rather it isomerizes into a cyclic oxepine structure. Steric effects precluded this isomerization from occurring when DFRC was applied to milled wood lignin. Instead, monoacetylated biphenolic moieties were released and quantified by (31)P NMR, at 4.3 dibenzodioxocin rings/100 C9 units. The dibenzodioxocin content in residual lignins isolated from kraft pulps delignified to various degrees showed that during pulp delignification, the initial rate of dibenzodioxocin removal was considerably greater than the cleavage rate of arylglycerol-beta-aryl ether bonds. The activation energy for the degradation of dibenzodioxocins under kraft conditions in milled wood lignin was 96 +/- 9 kJ/mol, similar to that of arylglycerol-beta-aryl ether bond cleavage.

Carbon Isotopes↗
PubMed2004

The behavior of deuterium-labeled monolignol and monolignol glucosides in lignin biosynthesis in angiosperms.

To examine the behavior of monolignol and monolignol glucosides in lignin biosynthesis, pentadeutero[9-D(2), 3-OCD(3)]coniferyl alcohol and pentadeutero[9-D(2), 3-OCD(3)]coniferin were synthesized and fed to growing Eucalyptus camaldulensis and Magnolia kobus. The differences in the incorporation patterns of these labeled precursors were studied using gas chromatography-mass spectrometry (GC-MS). Both precursors were incorporated into lignin, but the labeled coniferyl alcohol was incorporated more directly, resulting in a high proportion of pentadeutero-labeled guaiacyl and syringyl units in newly formed xylem, while labeled coniferin tended to be incorporated in lignin as tetradeutero units, especially in syringyl lignin in both trees. However, the incorporation efficiencies of the precursors into syringyl lignin were higher in Magnolia than in Eucalyptus, and the ratios of tetradeutero to pentadeutero in guaiacyl lignin were lower in Magnolia than in Eucalyptus when the trees were fed coniferin.

Cinnamates↗