OLIGOSACCHARIDE SYNTHESIS USING GLYCOSIDASES

A wide range of strategies may be considered for the synthesis of olig osaccharides in vitro using enzymes, all of which present significant challenges to the enzyme technologist. Many simple oligosaccharides ma y be produced by the hydrolysis of readily-available polysaccharides u sing specific enzymes. However, to produce the complex branched hetero -oligosaccharides of the types which occur N-linked to glycoproteins i s more taxing. Materials of this type may be synthesised using the nat ural synthetic enzymes which employ sugar nucleotides as substrates. T hese enzymes are highly specific but they are costly to use due to the ir instability and to the cost of their substrates. It has been demons trated that glycosidases are capable of synthesising hetero-oligosacch arides when provided with underivatised sugars in conditions of low wa ter activity but that the specificity of synthetic reactions is appare ntly not high and that yields of material are low. Approaches to these problems are discussed, including the use of immobilised enzymes in p acked-bed reactors to allow the 'ping' stage of the synthetic reaction to be separated in time from the 'pong' stage, and the application of aqueous two-phase systems which may be 'tailored' to separate the enz yme and the substrates from the final product. The ability to synthesi se a range of oligosaccharides is dependent on the availability of app ropriate glycosidases with differing specificities. There is a clear i mportance of 'biodiversity' in providing knowledge of sources of these .