Studies on the structure of yeast mannan. I. Purification and some properties of an alpha-mannosidase from an arthrobacter species.

A soil microorganism, designated Arfhrobacfer GJM-1, has been isolated which is capable of growing on Saccharomyces cerevisiae mannan as the carbon source. When grown on mannan, the microorganism secretes an a-mannosidase into the cultural medium. The enzyme is not found when mannose, glucose, or glycerol is substituted for mannan, but is present when oligosaccharides obtained by acetolysis of mannan are used as carbon sources. The cr-mannosidase has been isolated and partially purified. It was free of contaminating glycosidase, phosphatase, and protease activities. The enzyme is active on mannans from several different yeasts and on the oligosaccharides produced by acetolysis of yeast mannans, but has a low activity on cr-mannosides with aromatic or aliphatic aglycons. This is in contrast to results obtained with other cr-mannosidases and may reflect the different metabolic roles of the respective enzymes. The K, values for the di-, tri.-, tetra-, penta-, and hexasaccharides from S. cerevisiae mannan varied between 0.5 and 2 fll~. Because of the structural heterogeneity of these oligosaccharides, it is not certain what features contribute to the differences observed. The Km value for intact mannan was 1 X 10s6 M, but this value probably reflects the higher concentration of side chains in the mannan molecule.