Some properties of an endo-l,4-β-D-xylanase from the ligniperdous fungusTrametes hirsuta

Some properties of purified endo-l,4-β-D-xylanase (1,4-β-D-xylan xylanohydrolase, EC 3.2.1.8) from the ligniperdous fungusTrametes hirsuta were investigated. The enzyme was stable between pH 4.0 and 8.0 with optimum activity at pH 5.0–5.5. The temperature optimum was 50 °C and the enzyme was stable for up to 30 min at 45 °C; however, it was denatured at higher temperatures. TheK _m for 4-O-methylgluourono-D-xylan was 6.36. 10⁻³ equivalents ofD-xylose per litre, the activation energy was 28 kJ mol⁻¹. The molecular weight determined by means of gel chromatography was 22000–24000. The enzyme was activated by Ca²⁺ and inhibited by Ag⁺ and Hg²⁺. On the basis of the effect of 2-hy-droxy-5 nitrobenzyl bromide, N-bromosuccimmide and N-aeetyhmidazole it may be assumed that trytophan and possibly tyrosine residues influence the enzyme catalysis.