Dehydrogenative Polymerization Of Monolignols Research Articles

Effects of hemicelluloses on dehydrogenative polymerization of monolignols with cationic cell wall-bound peroxidase

To elucidate the influence of polysaccharides on hardwood lignification, dehydrogenative polymerization of monolignols, coniferyl alcohol (CA) and sinapyl alcohol (SA), was attempted with recombinant cationic cell wall-bound peroxidase (rCWPO-C) and horseradish peroxidase (HRP) in measurement cells of a quartz crystal microbalance with dissipation (QCM-D). Hardwood cellulose nanofibers were anchored; hemicelluloses, xylan, partially acetylated xylan (AcXY), galactoglucomannan, and xyloglucan, and the enzymes were subsequently adsorbed onto the QCM-D sensor surface, enabling fabrication of artificial polysaccharide matrices. The largest amount of rCWPO-C is found to be adsorbed onto AcXY among all the polysaccharides, which affords the largest amount and size of spherical dehydrogenation polymers (DHPs) from both CA and SA. In contrast, no DHP and a small amount of DHPs are formed from SA and CA, respectively, by HRP catalysis in all of the polysaccharide matrices. This study demonstrates important functions of a real tree-derived peroxidase, rCWPO-C, and AcXY for hardwood lignification.

Effect of pH on the Dehydrogenative Polymerization of Monolignols by Laccases from Trametes versicolor and Rhus vernicifera.

Dehydrogenative polymerization of coniferyl alcohol (CA) and sinapyl alcohol (SA) was conducted using commercial laccases, fungal laccase from Trametes versicolor (LacT) and plant laccase from Rhus vernicifera (LacR), at pH 4–7 to investigate how the enzymatic polymerization of monolignols differs between these two laccase systems. The enzyme activity of LacT was the highest at pH 4, whereas that of LacR was the highest at pH 7. A dehydrogenation polymer (DHP) was obtained only from CA in both laccase systems, although the consumption rate of SA was higher than that of CA. 1H–13C HSQC NMR analysis showed that DHPs obtained using LacT and LacR contained lignin substructures, including β-O-4, β-O-4/α-O-4, β-β, and β-5 structures. At pH 4.5, the β-O-4 structure was preferentially formed over the β-O-4/α-O-4 structure, whereas at pH 6.5, the β-O-4/α-O-4 structure was preferred. The pH of the reaction solution was more vital to affect the chemical structure of DHP than the origin of laccases.

Studies on the dehydrogenative polymerization of monolignol β-glycosides. Part 6: Monitoring of horseradish peroxidase-catalyzed polymerization of monolignol glycosides by GPC-PDA

Abstract Horseradish peroxidase (HRP)-catalyzed dehydrogenative polymerization of guaiacyl (G) and syringyl (S)-type monolignol γ-O-glucosides, isoconiferin (iso-G) and isosyringin (iso-S), which contain a hydrophilic glucosyl unit on γ-position of coniferyl alcohol and sinapyl alcohol, respectively, was monitored by gel permeation chromatography coupled with photodiode array detection (GPC-PDA). Contrary to the conventional dehydrogenative polymerization of monolignols, the polymerization of the glycosides produces water-soluble synthetic lignins (DHPs) in a homogeneous aqueous phase. Taking advantage of this unique reaction system, the method was developed to follow the changes of molecular weights in the course of DHP formations. Moreover, PDA detection permits determination of oligomeric S-type quinone methide intermediates (QMs) formed as stable transient compounds during polymerization of iso-S. A detailed comparison of the polymerization profiles revealed entirely different behaviors of G- and S-type monomers. The data strongly support the view that the low reactivity of oligomeric S-type QMs impedes the formation of DHPs from S-type monomers. In copolymerization of G- and S-type monomers, it is conceivable that G-type phenolic hydroxyl groups serve as good nucleophilic reactants to scavenge S-type QMs resulting in efficient production of DHPs. As a consequence, the present approach can be a powerful tool to study the in vitro dehydrogenative polymerization providing further mechanistic insights into lignin polymerization in vivo.

Immunolocalization of an anionic peroxidase in differentiating poplar xylem

Peroxidases are the major candidate enzymes involved in dehydrogenative polymerization of monolignols. Peroxidases have the signal sequence at their N-terminus and this suggests that they are transported to extracellular spaces or developing cell walls. In this study, we focused on an anionic peroxidase isozyme encoded by prxA3a, which seems to be related to lignification. To investigate the localization of peroxidase in differentiating xylem cells of poplar (Populus sieboldii × Populus grandidentata), anti-PRX3 antibody was raised against the anionic peroxidase. Western blotting and peroxidase activity inhibition assay showed specificity of the antibody. Labeling by anti-PRX3 antibody was localized in vessels and fibers during the secondary wall formation and was observed along the plasma membrane beside the microtubules. The labeling was not seen in the cell wall, where localization of peroxidases was expected during lignification. The peroxidase isozyme, which is suggested to be involved in monolignol polymerization, is localized on the plasma membrane and its localization might be regulated by microtubules.

Suitability of Peroxidase-Suppressed Transgenic Hybrid Aspen (Populus sieboldii X Populus gradidentata) for Pulping

Summary Lignin content, lignin composition and lignin removal were investigated in hybrid aspen (Populus sieboldii X Populus gradidentata) with suppressed peroxidase (POX) contents, involved in the dehydrogenative polymerization of monolignols. No significant suppression of the lignin content of the transgenic hybrid aspen was observed, but one (POX 29) of the POX-suppressed hybrid aspen species had a lower lignin content and gave a higher pulp yield at the same lignin content in kraft pulping than the control wild type. The molecular weight distribution of kraft lignins, sugar compositions and yields of nitrobenzene oxidation products of the transgenic woods were not different from those of the wild-type wood. These results indicate that suppression of POX may hold promise for producing woods suited for milder kraft pulping conditions using less chemicals and lower pulping temperature.

Characteristics of Lignin Structural Conversion in a Phase-Separative Reaction System Composed of Cresol and Sulfuric Acid

The chemical structures of lignocresols derived from native lignins by the phase-separative treatment with cresol and sulfuric acid were characterized by spectral analyses and chemical degradations. The changes in the structure of lignin during the conversion process were discussed. Lignocresol had few conjugated systems, being pinkish white, its brightness comparable to milled wood lignin. Spruce lignocresol included 0.64 mol/C 9 of cresolic nuclei in the molecule (0.9 mol/C 9 in birch lignocresol), 77% of which were linked to lignin Cα-positions through carbon-carbon linkages, 16% possibly to Cγ-positions, and the remaining 7% etherified to lignin side chains through its phenolic hydroxyl groups. The molecular weight (Mw) of lignocresol was ca. 3500 in spruce, lower in birch. Most of the β- and γ-positions in the side chains of C 9 units remained intact, except the coniferyl alcohol and aldehyde units. These structural features were constant during the reaction time up to 60min. It is concluded that the fragmentation of lignin in the phase-separative reaction system was principally due to the cleavage of benzyl aryl ethers, and the skeleton of lignocresol represents those of lignin subblocks formed by the dehydrogenative polymerization of monolignols.

Dehydrogenative Polymerization of Monolignols by Peroxidase and H2O2in a Dialysis Tube. II. Estimation of Molecular Weights by Thermal Softening Method

Dehydrogenative Polymerization of Monolignols by Peroxidase and H₂O₂in a Dialysis Tube. II. Estimation of Molecular Weights by Thermal Softening Method