beta-Mannosidase from the mushroom Polyporus sulfureus

Abstract

beta-D-Mannosidase (EC 3.2.1.25), a useful tool for the structural studies of heterosaccharide chains, has been isolated in a highly purified form from the fruiting bodies of the mushroom Polyporus sulfureus. This mushroom is unique among reported sources of this enzyme in that it has the advantage of being almost free of alpha-mannosidase activity. The purification procedure involves ammonium sulfate fractionation followed by Sephadex G-100 filtration and chromatography on columns of DEAE-cellulose and hydroxylapatite. The final enzyme preparation gives essentially a single band on disc gel electrophoresis. The purified enzyme liberates the beta-D-mannopyranosyl unit from various natural substrates such as the core glycopeptide, Man(GlcNAc)2-Asn isolated from ovalbumin, from Taka-amylase A, and from human alpha1-acid glycoprotein. It also hydrolyzes (Man)2-GlcNAc from the urine of an alpha-mannosidosis patient, 1,4-D-mannobiose and mannotriose isolated from ivory nut mannan, 4-O-beta-D-mannopyranosyl-L-rhamnose, 6-O-beta-D-mannopyranosyl-D-galactose and 4-O-beta-D-mannopyranosyl-N-acetylglucosamine. The molecular weight of this enzyme is estimated to be about 64,000 by gel filtration. For p-nitrophenyl-beta-D-mannopyranoside, the pH optimum is between 2.4 and 3.4 and the Km is 1.6 mM.