Glycosidases specificities

The question of a correlation of anomeric specificity of glycosidases with their susceptibility to aldonolactone inhibition was addressed by Reese and coworkers in a comparative study with six fungal a-D-glucosidases and... 

Specific glycosidases. Based on their reactivity with the respective 2-deoxy-2-fluoro-o - and -y -D-glycosyl fluorides, the enzymes were found to fall into three groups. 

Kinetic Constants for the Inactivation of Glycosidases by Conduritol Epoxides Corresponding to their Respective Glycon Specificities (see Text)... 

Scheme 6. — Reaction of ConduritoJ Epoxide (Anhydro-inositol, Hydroxyl groups omitted) with / - and a-Specific Glycosidase, Respectively.

The structures of many oligosaccharide chains can be elucidated by gas-liquid chromatography, mass spectrometry, and high-resolution NMR spectrometry. Glycosidases hydrolyze specific linkages in oligosaccharides and are used to explore both the structures and functions of glycoproteins. 

A detailed study of the 0-linked oligosaccharides present on the surface of normal granulocytes, chronic myelogenous leukemia cells, and acute myelogenous leukemia cells has been completed. Structures were elucidated by f.a.b.-m.s. after permethylation, and methylation analysis before and after specific exo-glycosidase treatments. Some of the components were shown by f.a.b.-m.s. to be poly(N-acetyllactosaminyl) oligosaccharides, for example, 29. 

Since a few years, new activities have been discovered in relation with fruit cell wall architecture, like new pectinases [1] (i.e. rhamnogalacturonase for the apple) new glycosidases [2](i.e. apiosidase for the grape). The improvement of the knowledge of fruit composition, cell wall chemistry, enzymology of endogenous and exogenous enzymes allow to supply the juice producers with preparations more and more purified and specific, blended in optimal combinations. 

Glycosidases are rather undemanding in the choice of substrates, which greatly broadens their applications compared to glycosyltransferases. However, they also suffer from several significant drawbacks, such as low regioselectivity and yields. Thus, the choice of an appropriate attitude and an enzyme type remains strongly dependent on the specific application. 

The synthesis of complex carbohydrate structures can preferably be accomplished using several enzymes in one-pot or sequential mode. Crude intermediate products may be either directly processed by the follow-up enzyme, or a fast and simple purification step may be included like desalting, concentrating, etc. This approach saves both time and costs, however, it requires a relatively high specificity, regioselectivity and yields in all the steps, which somehow limits the choice of glycosidases available. 

The specificity of glycosidases towards glycosyl acceptors is very broad. The structure of the acceptor molecule influences both the yield and the regioselectivity of glycosylation. 

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