The mechanism of action of glycosidases.

The factors that may contribute to the rate enhancement observed with enzymatic versus non-enzymatic hydrolysis of glycosides are discussed. The nature of the active site as deduced from labelling studies with beta-glucosidases is described. A two-step mechanism involving either an enzyme stabilized glycosyl ion or a covalent glycosyl-enzyme intermediate is proposed. Experiments with a beta-glucosidase from almonds show that even with 2-deoxy glucosides with good leaving groups as aglycon which are hydrolyzed 1000 times more slowly than the corresponding glucosides, the deglucosylation step is faster than the cleavage of the glycosidic bond.