Aryl-alcohol oxidase protein sequence: a comparison with glucose oxidase and other FAD oxidoreductases.
(33/871)
Aryl-alcohol oxidase (AAO), an FAD-dependent enzyme involved in lignin degradation, has been cloned from Pleurotus eryngii. The AAO protein is composed of 593 amino acids, 27 of which form a signal peptide. It shows 33% sequence identity with glucose oxidase from Aspergillus niger and lower homology with other oxidoreductases. The predicted secondary structures of both enzymes are very similar. For AAO, it is predicted to contain 13 putative alpha-helices and two major beta-sheets, each of the putative beta-sheets formed by six beta-strands. The ADP binding site and the signature-2 consensus sequence of the glucose-methanol-choline (GMC) oxidoreductases were also present. Moreover, residues potentially involved in catalysis and substrate binding were identified in the vicinity of the flavin ring. They include two histidines (H502 and H546) and several aromatic residues (Y78, Y92 and F501), as reported in other FAD oxidoreductases. (+info)
Effects of two types of dietary fibre on faecal steroid and lipid excretion.
(34/871)
Fibre supplements from wheat bran and sugar cane residue (bagasse) were added to the normal diet of volunteers for 12-week periods in a controlled metabolic study. Stool weights and stool fat excretion increased on both dietary fibres. Bagasse increased the daily loss of acid steroids, but bran failed to affect bile acid excretion. Decreased transit time without alteration in faecal flora occurred with bagasse. The raised excretion of bile acids and fatty acids failed to lower the plasma cholesterol and triglycerides after 12 weeks. Thus different fibre sources with variable components have dissimilar metabolic effects. (+info)
Is cellobiose dehydrogenase from Phanerochaete chrysosporium a lignin degrading enzyme?
(35/871)
Cellobiose dehydrogenase (CDH) is an extracellular redox enzyme of ping-pong type, i.e. it has separate oxidative and reductive half reactions. Several wood degrading fungi produce CDH, but the biological function of the enzyme is not known with certainty. It can, however, indirectly generate hydroxyl radicals by reducing Fe(3+) to Fe(2+) and O2 to H2O2. Hydroxyl radicals are then generated by a Fenton type reaction and they can react with various wood compounds, including lignin. In this work we study the effect of CDH on a non-phenolic lignin model compound (3,4-dimethoxyphenyl glycol). The results indicate that CDH can affect lignins in three important ways. (1) It breaks beta-ethers; (2) it demethoxylates aromatic structures in lignins; (3) it introduces hydroxyl groups in non-phenolic lignins. The gamma-irradiated model compound gave a similar pattern of products as the CDH treated model compound, when the samples were analyzed by HPLC, suggesting that hydroxyl radicals are the active component of the CDH system. (+info)
Essential role of caffeoyl coenzyme A O-methyltransferase in lignin biosynthesis in woody poplar plants.
(36/871)
Caffeoyl coenzyme A O-methyltransferase (CCoAOMT) has recently been shown to participate in lignin biosynthesis in herbacious tobacco plants. Here, we demonstrate that CCoAOMT is essential in lignin biosynthesis in woody poplar (Populus tremula x Populus alba) plants. In poplar stems, CCoAOMT was found to be expressed in all lignifying cells including vessel elements and fibers as well as in xylem ray parenchyma cells. Repression of CCoAOMT expression by the antisense approach in transgenic poplar plants caused a significant decrease in total lignin content as detected by both Klason lignin assay and Fourier-transform infrared spectroscopy. The reduction in lignin content was the result of a decrease in both guaiacyl and syringyl lignins as determined by in-source pyrolysis mass spectrometry. Fourier-transform infrared spectroscopy indicated that the reduction in lignin content resulted in a less condensed and less cross-linked lignin structure in wood. Repression of CCoAOMT expression also led to coloration of wood and an elevation of wall-bound p-hydroxybenzoic acid. Taken together, these results indicate that CCoAOMT plays a dominant role in the methylation of the 3-hydroxyl group of caffeoyl CoA, and the CCoAOMT-mediated methylation reaction is essential to channel substrates for 5-methoxylation of hydroxycinnamates. They also suggest that antisense repression of CCoAOMT is an efficient means for genetic engineering of trees with low lignin content. (+info)
Identification of glucosyltransferase genes involved in sinapate metabolism and lignin synthesis in Arabidopsis.
(37/871)
Sinapic acid is a major phenylpropanoid in Brassicaceae providing intermediates in two distinct metabolic pathways leading to sinapoyl esters and lignin synthesis. Glucosyltransferases play key roles in the formation of these intermediates, either through the production of the high energy compound 1-O-sinapoylglucose leading to sinapoylmalate and sinapoylcholine or through the production of sinapyl alcohol-4-O-glucoside, potentially leading to the syringyl units found in lignins. While the importance of these glucosyltransferases has been recognized for more than 20 years, their corresponding genes have not been identified. Combining sequence information in the Arabidopsis genomic data base with biochemical data from screening the activity of recombinant proteins in vitro, we have now identified five gene sequences encoding enzymes that can glucosylate sinapic acid, sinapyl alcohol, and their related phenylpropanoids. The data provide a foundation for future understanding and manipulation of sinapate metabolism and lignin biology in Arabidopsis. (+info)
Degradation of bisphenol A by the lignin-degrading enzyme, manganese peroxidase, produced by the white-rot basidiomycete, Pleurotus ostreatus.
(38/871)
Degradation of 2,2-Bis(4-hydroxyphenyl)propane (bisphenol A, BPA), an endocrine-disturbing chemical, by the growing mycelia of the white-rot basidiomycete, Pleurotus ostreatus, was examined. About 80% of BPA initially present decreased in 12 days of culture with this fungus. By in vitro experiments using the lignin-degrading enzyme manganese peroxidase (MnP), BPA was metabolized to phenol, 4-isopropenylphenol, 4-isopropylphenol, and hexestrol. The degradation products of BPA were assumed to be formed by the one-electron oxidation of the substrate. (+info)
Rapid dye decolorization method for screening potential wood preservatives.
(39/871)
We developed a new screening method for potential wood preservatives based on decolorization of the dye Remazol Brilliant Blue R by extracellular oxidative agents produced by wood decay fungi. Oxidative biodegradation of lignin yielded decolorized zones around and under fungal cultures on a dyed agar medium. Inhibitory effects were detected by direct observation and measurement of the decolorized zones. (+info)
Feasibility of using lignin isolated from forages by solubilization in acetyl bromide as a standard for lignin analyses.
(40/871)
Lignin concentration can be measured in plants by the acetyl bromide-soluble lignin spectrophotometric method; however, as with any spectrophotometric method, a reliable standard is needed. In the present experiments, lignin was extracted from each of the forages under study with the acetyl bromide reagent. The lignin isolated with acetyl bromide (LIAB) was then used as the reference standard in the acetyl bromide-soluble lignin (ABSL) analysis, which was compared with the acid detergent lignin (ADL) and potassium permanganate lignin (PerL) lignin analyses. Two maturity stages of each of the following forages were analyzed: Medicago sativa, Cynodon dactylon var. Coastal, Panicum maximum var. Centenario and var. Coloniao, Cynodon plectostachyus, Pennisetum purpureum, Setaria nandi, and Avena sativa. In addition, one wood sample, Eucalyptus sp., was analyzed. In general, ABSL values were highest (P < 0.001), followed by PerL and ADL, which also differed from each other (P < 0.001). Correlations with in vitro dry matter digestibility of samples were highest with the ABSL method. Absorption spectra of LIAB, either from plants of different maturity stages or from different vegetable species, suggested the presence of differences among some of the lignins. (+info)