Xylosidases

Other inverting glucosidases which conform to the pattern of direct hydrolysis of glycosyl fluorides having the correct anomeric configuration, and transglycosylation with inversion if the anomeric configuration is opposite to that of the natural substrates are trehalase from rabbit renal cortex and from the yeast Candida tropicalis, and ) -D-xylosidase from Bacillus pu-milis. ... 

The rapid inactivation of human lysosomal / -D-galactosidase is noteworthy, as the reaction had to be carried out at 2 pH units above its pH optimum (pH 4.0) in order to minimize the spontaneous decomposition of the inhibitor. Similar conditions had to be employed for ) -D-xylosidase from Penicil-lium wortmamii (optimum at pH 3.5), which was studied at pH 7.0. 

S-D-Xylosidase in extract from Trichoderma reesei Transxylosylation with methyl-/i-xyloside and 1 -butanol Butanol-acetate buffer pH 4.5 Kinetically controlled process 128... 

Redox reaetions and hydrolysis are the predominant metabolie eonversions triggered by the intestinal microflora. The main reductive enzymes produeed by the intestinal mieroflora are nitroreductase, deaminase, urea dehydroxylase, and azoreduetase the hydrolytic enzymes are P-glucoronidase, P-xylosidase, P-galaetosidase, and a-L-arabinosidase. Studies conducted by Macfarlane and co-workers have shown that proteolysis ean also happen in the colon [31]. More recent findings by this group indieate that bacterial fermentation of proteins in humans could account for 17% of... 

Brunner F et al (2002) A 6-glucosidase/xylosidase from the phytopathogenic oomycete,... 

Endoxylanase produced by a transformant strain of Escherichia coli has been shown to decrease the kappa number and increase the brightness of pulp in an enzymatic pretreatment followed by chemical extraction (27). Beta-xylosidase, on the other hand, had no effect in the treatment. The mannanase produced by Bacillus suhtilis was found to be equally effective as the xylanase. The specificities of mannanases produced by two different organisms, however, differed considerably 49). Enrichment of the culture broth of Streptomyces olivochromogenes, containing mainly endoxylanase, with different pure enzymes or enzyme mixtures acting on side chains and other hemicelluloses, resulted only in slight increases in brightness and in kappa number reduction (55). 

Xylans are heteropolysaccharides which are depolymerized by j8-l,4-D-endoxylanases. Due to the abundance and variety of substituents in native xylans, different accessory enzymes are also needed for the total hydrolysis of xylan. The knowledge of a-glucuronidase, a-arabinosidase, and acetyl xylan- and feruloyl esterases has increased considerably in recent years. In addition to acting in synergism with endoxylanases and )8-xylosidase for the complete hydrolysis of xylan, some of these accessory enzymes are also capable of changing the structure of polymeric xylans. 

Exo-l,4-j8-D-xylosidases (EC 3.2.1.37) hydrolyze xylooligosaccharides and xylobiose to xylose by removing successive D-xylose residues from the nonreducing termini. j8-Xylosidase is part of most microbial xylanolytic systems, but the highest extracellular production levels have been reported for fungi. 

Synergism between a-arabinosidase, xylanase and j8-xylosidase has been demonstrated in the hydrolysis of wheat straw arabinoxylan with purified enzymes of T, reesei (71). > en only xylanase and )8-xylosidase were used in the hydrolysis, the xylose yield was only 66% of that produced by the whole culture filtrate at the same activity levels of these two enzymes, and no arabinose was produced. Addition of a-arabinosidase increased the yields of both xylose and arabinose. Enhanced hydrolytic action of hemicellulolytic or pectinolytic enzymes in the hydrolysis of alfalfa cell wall polymers by addition of Ruminococcus albus a-arabinosidase has also been reported (37). 

This enzyme [EC 3.2.1.37], also referred to as xylan 1,4-)3-xylosidase and exo-l,4-/3-xylosidase, catalyzes the hydrolysis of l,4-)3-D-xylans resulting in the removal of successive o-xylose residues from the nonreducing termini. Xylobiose can also be utilized as a substrate. The sheep liver enzyme has been reported to exhibit other exoglycosidase activities. 

RIBULOSE-5-PHOSPHATE 4-EPIMERASE a-XYLOSIDASE j8-XYLOSIDASE d-XYLULOKINASE l-XYLULOKINASE X-Pro dipeptidase... 

This important concept was rapidly absorbed by the research community, providing fine-tuning of both glycosidase categorization and inhibitor design. In particular, subtle differences of xylosidase and xylanase specificities were probed, and they provided useful insights into the complex and finely tuned enzymatic hydrolysis of glycosides. 

Family 10 xylanase Cex from Cellulomonas fimi and family 11 xylanase Bex from Bacillus circulans198,199 (the first being an anti-, the second a syn-protonator) were exposed to deoxynojirimycin-related (80, Scheme 22) and isofagomine analogous (81) xylosidase inhibitors, along with the anti-protonation-selective xylobiosyl... 

V. Patel and A. L. Tappel, Identity of P-glucosidase and P-xylosidase activities in rat liver lysosomes, Biochim. Biophys. Acta Enzymol., 191 (1969) 653-662. 

This requires hydrolysis, and fermentation or transformation steps. While enzymes degrading the heteroxy-lan are known as xylanases, they also require the additional actions of / -xylosidases, a-arabinosidases, a-glucuronidases and certain esterases for total hydrolysis. 

The xylanolytic enzyme system of Trichoderma reesei, a well-known producer of cellulolytic enzymes, is versatile and well suited for the total hydrolysis of different xylans. It consists of two major, specific and several non-specific xylanases, at least one / -xylosidase, a-arabinosidase and a-glucuronidase and at least two acetyl esterases. The hydrolysis of polymeric xylans starts by the action of endoxylanases. The side-groupcleaving enzymes have their highest activities towards soluble, short xylo-oligosaccharides, and make the substituted oligosaccharides again accessible for xylanases and / -xylosidase. 

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