Isolation of an α-Mannosidase Which Hydrolyzes Yeast Mannan

A soil microorganism has been isolated which will grow on yeast mannan as the sole carbon source. The organism secretes into the cultural medium an α-mannosidase which appears to act as an exoglycosidase and removes the short α-1,2′- and α-1,3′-linked mannose side chains of the mannan molecule to leave a resistant core composed of a linear α-1,6′-linked mannose polymer. This provides the first direct proof that yeast mannan contains such a backbone structure. While the mannosidase does not appear to degrade the 1,6′-linked backbone, it does hydrolyze α-1,6′-mannobiose as well as the α-1,2′ and α-1,3′-linked oligosaccharides obtained from yeast mannan by acetolysis. It is not yet known whether this reflects a broad substrate specificity or the presence of several different proteins in the preparation. The enzyme may be useful for studies on the yeast cell wall and on mannose-containing glycoproteins.