APPLICATIONS OF HYDROLYTIC AND DECARBOXYLATING ENZYMES IN BIOTRANSFORMATIONS

Peptides, and oligosaccharides and glycosides, can be synthesised by making use of the 'reverse hydrolytic activity' of proteases and glycosidases respectively. In applying these enzymes to the practical synthesis of these classes of compound, several factors need to be considered, namely the need to shift the rate-determining step through the use of activated substrates, the need to minimise competing hydrolysis of these and the need to minimise hydrolysis of the products. In spite of these problems, the enzymatic methods have many attractive features, not least amongst which is the absolute control of stereochemistry in acyl transfer and glycosyl transfer respectively. Enzymes (lyases) that normally catalyse the cleavage of carbon-carbon bonds have been found to catalyse also their formation by 'abnormal' pathways. These enzymes are pyruvate decarboxylase (EC 4.1.1.1) and acetolactate decarboxylase (EC 4.1.1.5). A third enzyme, acetolactate synthase (EC 4.1.3.18), that catalyses carbon-carbon bond formation in the pathway of biosynthesis of the branched-chain amino acids, has a limited substrate range but its mode of action is of interest as it is homologous with pyruvate decarboxylase. This observation sheds light on the 'abnormal' reaction catalysed by pyruvate decarboxylase.