3-Glucuronidase action

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. 

Glucuronidase in dog tissues191 and in Helix pomatia preparations87 may also be subject to its action. 

One might be more inclined to attach significance to this inhibitor as a means of physiological control if there were tissues that lacked it but contained susceptible enzyme. In any case, the action of this inhibitor does not explain the changes in (8-glucuronidase activity that are seen in vivo.9... 

In the belief that the action of the enzyme might be modified by the presence of some of the more prevalent metals in trace amounts, the effects of cations on mammalian /3-glucuronidase were re-investigated186 195 of a large number studied, only Cu , Ag , and Hg were pronounced in their effects. (Inhibition was also seen with uranium acetate, ammonium chloroplatinate, osmium tetroxide, and sodium tungstate.83) Marked inhibition was seen with 2.5 X 10-6 M of Ag and 1.5 X 10 6 M of Hg00, and inhibition by these two ions was reversed by tissue constituents. 

It seems feasible that traces of heavy-metal ions may have some bearing upon certain features of the action of mammalian /3-glucuronidase, such as the fall in net activity seen on dilution of highly purified preparations (see Section IV), the inhibitory action of the unknown constituents of urine,185 190 and the pH optimum at pH 3.4 observed by Mills, Paul, and Smith166 but by no other workers (see Section VI). The presence of traces of Cu in the assay mixture would provide a completely satisfactory explanation of the variable effects reported with L-ascorbic acid (see Section IX, 2).196s... 

Strictly speaking, an enzyme can only provisionally be classified as a /8-glucuronidase before its action has been shown to be purely hydrolytic— by the isolation of D-glucuronic acid as well as the aglycon. This consideration is of particular importance when whole, bacterial suspensions are employed as a source of the enzyme. 

Unlike starch or cellulose, BSG hemicellulose has a complex structure, which is still present, in part, on its autohydrolysis products. Oligosaccharides from BSG hydrolysis consist mainly of branched arabino-xylo-glucurono oligosaccharides that are not highly acetylated when compared to other xylans, such as from Eucalyptus wood (31). The action of several enzymatic activities including endo-l,4-P-xylanase P-xylosidase and accessory activities such as acetyl xylanesterase, a-glucuronidase, and a-arabino-furanosidase is therefore required for the complete hydrolysis of OCL to monosaccharides. 

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