PHYSICOCHEMICAL AND CATALYTIC PROPERTIES OF A LOW-MOLECULAR-WEIGHT ENDO-1,4-BETA-D-XYLANASE FROM MYROTHECIUM-VERRUCARIA

A low-molecular-weight endo-beta-1,4-D-xylanase (endo-beta-1,4-D-Xylan xylanohydrolase; E.C. 3.2.1.8) isolated from solid-state cultures of Myrothecium verrucaria has M(r) and pI values of 15,900 and 4.35, respectively, and a carbohydrate content of 11% (w/w). The enzyme is most active at pH 5.5 and 45-degrees-C, and has a half-life of 16 min at pH 5, 50-degrees-C. It catalyzes the hydrolysis of various beta-1,4-linked and mixed (1,3; 1,4)-linked beta-glucans, but kinetic parameters showed it to be primarily a xylanase. Inhibition studies suggested the possible involvement of arginine, cysteine, histidine, tryptophan, and a carboxylate(s) in binding or catalysis. The pattern of products of hydrolysis of various xylans and of xylopentaose clearly demonstrated the purified enzyme to be an endo-beta-1,4-xylan xylanohydrolase (E.C. 3.2.1.8).