APPLICATIONS OF HYDROLYTIC AND DECARBOXYLATING ENZYMES IN BIOTRANSFORMATIONS

Peptides, and oligosaccharides and glycosides, can be synthesised by m aking use of the 'reverse hydrolytic activity' of proteases and glycos idases respectively. In applying these enzymes to the practical synthe sis of these classes of compound, several factors need to be considere d, 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) tha t normally catalyse the cleavage of carbon-carbon bonds have been foun d to catalyse also their formation by 'abnormal' pathways. These enzym es are pyruvate decarboxylase (EC 4.1.1.1) and acetolactate decarboxyl ase (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 biosynt hesis of the branched-chain amino acids, has a limited substrate range but its mode of action is of interest as it is homologous with pyruva te decarboxylase. This observation sheds light on the 'abnormal' react ion catalysed by pyruvate decarboxylase.