Lignin bound residues

D, which Is structurally similar to MCPA, appeared to be Inco-porated into lignin (255). This was in sharp contrast to MCPA metabolism in wheat. Carboxln (aniline-l4C) metabolism in peanut cell suspension culture and the fruit of whole peanut plants is an example of tissue variation. In peanut cell suspension culture, only 2.7% of the carboxln was incorporated Into bound residue, but In the fruit of whole plants, 21% Incorporation into bound residue was observed (121). The metabolism of metrlbuzln In tomato and soybean Is an excellent example of species variation. In tomato, metrlbuzln was rapidly metabolized to N-glucosldes and only 2% was Incorporated into bound residue, but In soybean, metrlbuzln was metabolized slowly by homoglutathione conjugation and 20-30% of the metrlbuzln was incorporated into bound residue (46.95). 

Zitzelsberger, W., W. Ziegler, and P.R. Wallnofer. 1987. Stereochemistry of the degradation of veratrylglycerol-(3-2,4-dichlorophenyl-ether, a model compound for lignin bound xenobiotic residues by Phenerochaete chrysosporium, Corynebacterium equi and photosensitized rioboflavin. Chemosphere 16 1137-1142. 

As can be seen from Fig 2b, the solid state C-13 nmr spectrum of T. aestivum also shows sets of enhanced resonances at 61 ppm and 169.6-174.9 ppm respectively (24). However, their relative intensities are very different from that observed for L. leucocephala. Indeed, it can immediately be seen that very little reduction of the administered precursor to hydroxymethyl analogues (at 61 ppm) has occurred. On the other hand, the dominant resonances at 169.6 and 174.9 ppm are coincident with bound hydroxycin-namic acids (e.g. ferulic 5a) and its esters (31). Subsequent analysis of its isolated acetal lignin derivative (32) indicated that much of the lignin contained hydroxycinnamate residues (33). 

Fig. 3.6 Solvent access surfaces (colors represent electrostatic potentials) showing the exposed tryptophan residue (as yellow van der Waals spheres) involved in oxidation of lignin and other high redox-potential substrates by VP (a) and LiP (b). Lignin can be directly oxidized by VP at the tryptophan radical, while LiP requires the simultaneous presence of VA (synthesized by the fungus) acting as an enzyme-bound mediator [74]. Based on VP and LiP crystal structures (PDB 2BOQ and 1LLP, respectively)...

FIGURE 11.23 Successive decrease of aromatic methoxyl groups and organically bound chlorine in the residual fiber lignin when a softwood kraft pulp is bleached according to the sequence OD(EO)DD. 

The three principal components of plant materials are cellulose, lignin, and hemi-cellulosics. Cellulose and hemicellulosics are polysaccharides. Cellulose is a highly regular structure, crystalline polymer, made up of thousands of glucose residues, covalently bound head-to-tail (Fig. 3.1). 

No active substance could be detected in plants treated with carboxin six weeks after the treatment. The major part of the residue found was sulfoxide. Actually, sulfoxide can occur in the plant in two ways. On the one hand, carboxin is oxidised relatively rapidly in the soil, and the plant takes up its sulfoxide, and, on the other hand, carboxin is metabolised within the plant to sulfoxide, presumably by enzyme systems producing hydrogen peroxide, such as riboflavin or flavin enzymes (Lyr et al., 1975a). It has been proved by extraction with hot dimethyl sulfate that sulfoxide formed in the plant is gradually bound in the form of a water-insoluble complex to lignin and is thus detoxified. No hydrolysis of carboxin in the plant has been observed (Chin et al., 1973). 

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