Purification, Characterization, and a Potential Application of .BETA.-Glucosidase from Aspergillus pulverulentus YM-80

Abstract

A fungus, strain YM-80, isolated from a soil sample produced β-glucosidase ( β-D-glucoside glucohydrolase EC 3.2.1.21) in solid culture. The fungus was identified as Aspergillus pulverulentus from its taxonomical characteristics. The β-glucosidase was purified 18-fold from the culture extract by (NH4)2SO4 precipitation, DEAE-Toyopearl 650M, Butyl-Toyopearl 650M and Sephacryl S-200 chromatography. The purified enzyme appeared as a single band on SDS-PAGE. The molecular weight of the purified enzyme was estimated to be 118,000 by SDS-PAGE and 240,000 by gel filtration. The enzyme was an acidic protein with a pI of 4.5 and the specific activity was 308 U/mg protein. The optimum temperature and pH for the enzyme activity were 60°C and 4.0, respectively. This enzyme was stable in the pH range 3.0-7.0 and also up to 50°C. The activity of the enzyme was completely inhibited by Hg2+ and SDS. The purified enzyme was active with a broad range of β-linked glucosides but not α-linked saccharides. Added during tofu processing, the enzyme was useful for the preparation of aglycon isoflavone-enriched tofu by hydrolysis of the glucoside form. However, isoflavones with 6"-O-acetyl and 6"-O-malonyl glucosides were not converted into the aglycon form.