Polysaccharides hydrolases

Due to the extreme variety of xylan structures, it is obvious that many kinds of enzymes are needed for their complete hydrolysis in nature. Xylanases (EC 3.2.1.8.) are the polysaccharide hydrolases responsible for the attack of the polymer backbone itself. The total hydrolysis or modification of heteroxylans requires in addition several different exo-glycosidases and esterases. The present knowledge of these enzymes is reviewed in this paper. 

The scheme proposed above requires microbial colonization of the material and excludes degradation by amylases and cellulases that are present in soils (28), but are not newly synthesized or associated with microbial cells. Active polysaccharide hydrolases are found in nearly all soils, but these enzymes are primarily bound to soil organic matter or mineral components attachment is firm enough to severely limit migration of the enzymes from surrounding soil to the film. 

A oligosaccharide that cannot be degraded further by a polysaccharide hydrolase or polysaccharide phosphoryl-... 

Two hypotheses on the nature of these auxin-induced reactions within the wall have received major attention. The first conceives of a change in wall synthesis, either in amount or pattern of deposition the second ascribes loosening to the action, at lowered pH, of polysaccharide hydrolases that are induced by auxin. 

Some polysaccharide hydrolases also catalyze glycosyl transfer. 

They are considered separately from the polysaccharide hydrolases, but are closely related to them, both mechanistically and structurally. In glycosyl transfer the acceptor water is replaced by a hydroxy group provided by an oligo- or polysaccharide. 

In J6>-cleavage the enzyme first attacks at an interior glycosidic linkage in the substrate. The (io-hydrolases are widely represented among the polysaccharide hydrolases and lyases. The cleavage may represent a single productive encounter with the substrate, so that both polymer fragments are released from the enzyme. This action pattern has been described as multi-chain attack (O Fig. 4) [37]. 

Lysozyme is unique among the polysaccharide hydrolases in that its chemical (107) and physical (24, 25, 173, 197) structure is accurately known and the mechanism of its hydrolytic action explained in considerable detail (182, 195, 221). Comparison of the characteristics of lysozyme action (Table V) with those of the -glucan endo-hydrolases (Table II) shows that these enzymes share many common features. 

Microbial polysaccharide hydrolases specific for cellulose, xylan, pectin,... 

Microbial 3-Glucan Hydrolases and Lysis of Plant Cell Wall Polymers. Many soil and aerial pathogens gain access to host tissues by enzymic lysis of epidermal cell walls of roots, leaves, stems, etc.. Phytopathogenic organisms possess an array of inducible polysaccharide hydrolases capable of degrading the complex polysaccharides of the plant cell wall (, 10). The... 

Hydrolases are also useful for elucidation of the primary structure of polysaccharides. Exo-hydrolases can be used as a sequencing tool (3), although their use may be limited to oligosaccharide-sequencing. Endo-hydrolases cleave bonds in the backbone of the polysaccharides. In this way, oligosaccharide fragments can be obtained that are relatively easy to characterise. Furthermore, polysaccharide-hydrolases can be used to obtain valuable mono- and oligosaccharides like L-rhamnose, cyclodextrins and trehalose... 

Since this is a book on nomenclature, it is a pity that Enzyme Nomenclature does not necessarily use nomenclature currently accepted on an official basis elsewhere. A good example is the area of glycoside hydrolases hydrolysing 0-glycosyl compounds where the recommended nomenclature is sometimes based on polysaccharide structure of the substrate, and sometimes on a trivial name non-indicative of substrate structure. Furthermore, exo- and e do-acting polysaccharide hydrolases are not necessarily distinguished, and in a few instances a singular enzyme activity is covered by more than one EC number. 

The following information on immobilized glycoside and polysaccharide hydrolases and carbohydrate isomerases and oxidases is worthy of note. a-Amylase, glucoamylase, and D-glucose isomerase have been immobilized by adsorption onto new matrices synthesized by copolymerization of hydroquinone and other phenolic compounds with formaldehyde or glutaraldehyde. The immobilized enzymes retain their activity in continuous use and high flow rates may be achieved in packed bed reactors, as the resin matrices are highly porous and hydrophilic. 

Polysaccharides are among the most important biopolymers as are proteins and nucleic acids in natin-e. They are regarded as three important families of natural biomacromolecules. As to the enzymatic polymerization for polysaccharides, hydrolases and transferases are reported to catalyze their synthetic reactions. 

A review of enzyme analysers has described the automation of fixed-time and continuous-monitoring assays and the uses of partly or completely automated analysers and multi-channel systems. Automated analyses of polysaccharide hydrolases, in soluble or insoluble form, have been based on determination of the liberated reducing sugars with 3,5-dinitrosalicylic acid. A sensitive and specific method for locating glycoside hydrolases (e.g. oc-D-mannosidases) in polyacryl-... 

New sensitive assays for dextranase activity are based on the use of Sephadex substituted with either 2,4,6-trinitrophenyl groups (for spectrophotometric assay) or fluorescamine groups (for fluorometric assay). 3,5-Dinitrosalicylic acid has been used in automated assays to determine the reducing sugars released on hydrolysis of the appropriate substrates with soluble or insoluble dextranases and other polysaccharide hydrolases. ... 

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