HUMAN LYSOSOMAL AND JACK BEAN ALPHA-MANNOSIDASES ARE RETAINING GLYCOSIDASES

The stereochemical course of the hydrolyses catalysed by two alpha-man nosidases has been determined directly by H-1 NMR. Synthetic substrate s were incubated with the enzymes and the anomeric configuration of th e initially formed product was ascertained in each case by observation of the chemical shift of the anomeric proton at the hemiacetal centre . Both mannosidases were found to catalyse hydrolysis with retention o f stereochemistry at the anomeric position. Human lysosomal alpha-mann osidase (a class II mannosidase) is a member of the glycosidase family 38 and thus has sequence similarity with several alpha-mannosidases r esponsible for glycoprotein biosynthesis. Jack bean alpha-mannosidase was shown to be mechanistically similar to the lysosomal enzyme and wi ll provide a useful model system in mechanistic studies and inhibitor design. (C) 1997 Academic Press.