Purification and characterization of a low-molecular-weight xylanase produced by Acrophialophora nainiana

A low-molecular-weight xylanase activity (XynI) was isolated from the fungu s Acrophialophora nainiana after growth in a solid medium containing wheat bran. XynI was purified to apparent homogeneity by ultrafiltration and gel filtration chromatography. The purified enzyme had a molecular weight value of approx. 17 kDa, as determined by SDS-PAGE. This enzyme was most active at 50 degrees C and pH 6.0. At 50 degrees C the half-life was 150 min. The apparent K-m value for birchwood xylan was much lower than the K-m value fo r oat spelt xylan. XynI was activated by L-cysteine, DTE, beta-mercaptoetha nol, and L-tryptophan. XynI did not show significant sequence homology with other xylanases. The analysis of hydrolysis products of xylans and wood pu lps showed that XynI was able to release xylooligomers ranging from X2 to X 3 and X2 to X6, respectively. The enzyme was not active against acetylated xylan. A small amount of xylose was released from deacetylated, birchwood, and oat spelt xylans. The results obtained with enzymatic treatment of Kraf t pulp indicated a reduction in the amount of chlorine compounds required f or the process and enhanced brightness gain.