GLYCOSIDE HYDROLASES - MECHANISTIC INFORMATION FROM STUDIES WITH REVERSIBLE AND IRREVERSIBLE INHIBITORS

This chapter discusses the results of the studies that permit some generalizations on the catalytic mechanism of glycoside hydrolases from widely differing sources and with different sugar and aglycon specificities and that have become available over the past 15 years. The strong inhibition of glycosidases by aldonolactones was first mentioned in 1940 by Japanese workers who studied β-D-glucosidases from Aspergillus (Taka-diastase) and almonds. Even though both of these groups of compounds are derived from normal substrates by only a minor modification of the glycon moiety, they are discussed together with pseudosubstrates because their reactions with glycosidases show, in many cases, unusual kinetic features. The information relevant to the mechanism of an enzyme-catalyzed reaction can, in general, only be obtained from irreversible inhibitors that react specifically at the active site, and thereby inactivate the enzyme. In many cases, inhibition studies were not carried out to obtain information on the reaction mechanism, but for other purposes. Thus, only inhibitors were tested that were considered suitable for the particular project, for example, studies on the biological function of the enzyme where glycosylamines and aldonolactones are unsuitable. © 1990 Academic Press Inc.