Heteropolysaccharides degradation

Pectin as one of the major plant cell wall constituents has received much attention both from a scientific and a technological point of view. Although pectin has been known to be a very complex heteropolysaccharide for quite some time, most progress on the elucidation of its structure has been attained in the last decade as a result of refinement and development of new more powerful techniques like HPAEC, HPGPC, NMR and the application of purified enzymes able to degrade specific parts of the complex molecule. 

During start-up, the microbial population distribution in the biofilm varies with time. Initial colonization of the particle may be by one or more species that alter the surface favorably for colonization by other species. For instance, in the operation of a butyrate-degrading fluidized bed bioreactor, methanogens attached to the sand particles early in the start-up process and produced a primary matrix of heteropolysaccharides that allowed attachment of other bacterial species (Sreekrishnan et al., 1991 Zellner et al., 1991 Yongming et al., 1993). This is contrary to findings in an acetate-propionate-butyrate degrading reactor, in which facultative anaerobes were found to be the initial colonizers (Lauwers et al., 1990). 

Detrimental effects in WPC, 96 Thermal degradation, 95 Hemicellulosic materials, 77, 92, 94, 95, 180 Hemp fiber, 82, 83, 86, 101, 110 Cellulose content, 110 Eiber diameter, 110 Lignin cintent, 110 Specific gravity, 110 Heteropolysaccharides, 92 High density polyethylene (HDPE), 52, 55, 67, 68, 363, 371,... 

The /8-eIiminative fragmentation of the heteropolysaccharide chain was first observed by K. Meyer and coworkers.- Sodium hyaluronate (26) was incubated with bacterial enzyme preparations obtained from Fhvo-bacterium. Staphylococcus aureus, and Clostridium welchii. All of these bacterial enzymes gave the same degradation product (27), which proved not to be identical with N-acetylhyalobiouronic acid.- ... 

The endocyclic, enolacetal-forming, 8-eliminative degradation of dermatan sulfate (33) possesses only one other notable stereochemical feature, namely, the hexopyranuronate residue of this heteropolysaccharide is that of L-idopyranuronic acid, in which the C-5 proton and the C-4 leaving-group are both axially attached (as was proved with synthetic, model compounds, discussed later) in the JC(l) conformation. Therefore, the /8-eliminative degradation of dermatan sulfate can be accepted as being a diaxial procedure, as in 38. 

This fragmentation of the heparin heteropolysaccharide chain proved to be a jS-elimination reaction in which diazomethane acts as the proton acceptor. It is interesting that aryldiazoalkanes (for example, phenyl or substituted-phenyl diazomethanes) cannot be used for a similar j8-eliminative degradation of quaternary ammonium salts of sulfated heteropolysaccharides. 

Hence, the stereochemistry of the 8-eliminative degradation of alginic acid seems to be similar to that of the heteropolysaccharide chain of heparin. As already described, in tbe latter 8-eliminative degradation, both the D-glucopyranuronate and the L-idopyranuronate, possessing the same stereochemical disposition of the groups on C-5 and C-4 of the ring, are involved. 

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