Purification of an acidic α- d-mannosidase from Aspergillus saitoi and specific cleavage of 1,2-α- d-mannosidic linkage in yeast mannan

Abstract

An acidic α- d-mannosidase (α- d-mannoside mannohydrolase, EC 3.2.1.24) has been isolated from culture filtrate of Aspergillus saitoi. The extracellular α-mannosidase was homogeneous in polyacrylamide gel electrophoresis. The molecular weight of the enzyme was 51 000 and the isoelectric point pH 4.5. The purified enzyme has a pH optimum of 5.0, a K m of 0.45 mM with baker's yeast mannan and has no activity towards p- nitrophenyl-α- d-mannoside . The mode of action of the enzyme has been studied with baker's yeast mannan and saké yeast mannan. The enzyme cleaves specifically the 1.2-α-linked side chain, producing free mannose.