Abstract
Proteases and glycosidases are classes of hydrolytic enzymes that are used in bio- transformations to catalyse the synthesis of peptides, and of glycosides and oligosaccharaides, re- spectively, by a reversal of their normal mode of action. The practical application of both methods shares several common features, namely the shift of rate-determining step through the use of ac- tivated substrates (aminoacyl and glycosyl donors respectively), the need to reduce or eliminate competing hydrolysis in the aminoacyl and glycosyl transfer steps, and the need to minimise hy- drolytic cleavage of the products. Control of these factors is illustrated by a method for peptide synthesis using a-chymotrypsin suspended in dichloromethane containing low concentrations of water and a method for disaccharide synthesis using an N-acetylgalactosaminidase from As- pergillus oryzae. Molecular modelling of the oxyanion intermediate has been found to explain a number of features of reactions catalysed by a-chymotrypsin and to predict others that were the subject of experimental test. The concept of anomeric control was used to modulate the re- gioselectivity of N-acetylgalactosaminyl transfer catalysed by the N-acetylgalactosaminidase.
Published Version
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