Hemicellulose depolymerization enzymes

Depolymerization of hemicellulosic structure is still being developed. Because of its more complicated structure involving several kinds of sugar units in variously linked conformations, more than one specific enzyme is needed. More simple plant starches can be effectively broken down to sugars with combinations of enzymes, including amylases and glucoamylases. 

Aphids have flexible, stylet-like mouthparts adapted for probing of plant tissues. By this means, the aphid must use chemical cues from the plant to determine if the plant is a suitable host (host plant quality), where the aphid is on the plant, the location of the stylet within the plant tissues, and the direction to probe to locate the plant phloem (Campbell and Dreyer, 1990 Dreyer and Campbell, 1987). Aphids avoid many of the toxic compounds stored in plant cells by probing between the cell walls. These insects are able to penetrate the intercellular spaces by producing a variety of digestive enzymes which depolymerize the pectins and hemicelluloses forming the intercellular-cell wall matrix. Aphid-host plant compatibility is associated to the extent that these enzymes depolymerize their respective substrates, and a reduced rate of depolymerization is often associated with host plant resistance. Differences in methoxylation, acetylation, or neutral sugar composition in the matrix polysaccharides are often involved in this reduced depolymerization. Further, specific breakdown products from depolymeri-... 

This chapter focuses on production of sugars from cellulosic or fibrous biomass feedstocks using conversion routes based on enzymatic hydrolysis. Section 4.2 describes the nature of cellulase and hemicellulase enzyme systems capable of depolymerizing cellulose and hemicellulose to soluble sugars, and reviews the prominent concepts of enzyme synergy and biomass recalcitrance. Performance of enzymatic hydrolysis under anticipated real-world processing conditions involving... 

Xylanases depolymerize hemicellulose and breaks the covalent bond between lignin and cellulose. The depolymerized hemicellulose and separated lignin may be removed exposing the celulosic fiber and increasing cellulose content. Cellulases are enzyme complexes including enzymes that attack the cellulose chains at random, that hydrolyze the cellulose chains from the end and that hydrolyze the cellulobiose into glucose [12]. Yilmaz [13] detected stronger effect of xylanases on fiber properties compared to that of cellulase enzymes. 

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