AN ACETYLGLUCOMANNAN ESTERASE OF ASPERGILLUS-ORYZAE - PURIFICATION, CHARACTERIZATION AND ROLE IN THE HYDROLYSIS OF O-ACETYL-GALACTOGLUCOMANNAN

An acetyl glucomannan esterase (AGME) was purified to electrophoretic homogeneity from the culture supernatant of Aspergillus oryzae. This n ew enzyme had a molecular mass of 36 kDa and an isoelectric point of 4 .6. It was most active in the pH range 5.0-5.5 and was stable for 24 h at 40 degrees C at pH 5.0-6.0. The purified esterase liberated acetic acid from O-acetyl-galactoglucomannan, O-acetyl-4-O-methylglucuronoxy lan and alpha-naphtyl acetate. The specific activity was 10-times high er for acetylated mannan than for acetylated xylan. The enzyme was abl e to act on polymeric substrate but activity was clearly enhanced by a ddition of mannanase from Trichoderma reesei and cr-galactosidase from guar seeds. Presence of mannanase also increased the liberation of ac etic acid in long-term hydrolysis (24 h), while the addition of alpha- galactosidase had no effect. No significant synergism between these tw o glycanases and the previously characterized esterase of A. oryzae (F E), which is also able to deacetylate galactoglucomannan, was observed . Even though the AGME had 8-times higher specific galactomannan deace tylating activity than the FE, the maximum amount of acetic acid liber ated from the polymeric galactoglucomannan by AGME was only 80% of tha t of FE. Bath esterases clearly enhanced the action of mannanase and c u-galactosidase in the degradation of O-acetyl-galactoglucomannan isol ated from Norway spruce.