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A low-molecular-weight endo-β-1,4- d -xylanase (endo-β-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°C, and has a half-life of 16 min at pH 5, 50°C. It catalyzes the hydrolysis of various β-1,4-linked and mixed (1,3; 1,4)-linked β-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-β-1,4-xylan xylanohydrolase (E.C. 3.2.1.8).

Two endo-β-1,4-xylan xylanohydrolases (EC 3.2.1.8), XynA and XynB, from solid-state cultures ofPenicillium capsulatum, were purified to apparent homogeneity as judged by electrophoresis and isoelectric focusing. Each is a single subunit glycoprotein. XynA containing 97 mol carbohydrate·mol−1 protein, while XynB contains 63 mol·mol−1.M r and pI values are 28 500, 5.0–5.2 (XynA) and 29 500, 5.0–5.2 (XynB), respectively. Both enzymes are most active at pH 4 and 47–48°C, and have half-lives of 32 min (XynA) and 13 min (XynB) at pH 4, 60°C. Each form catalyzed the hydrolysis of a variety of xylans, albeit with different degrees of efficiency. In addition, XynB catalyzed extensive degradation of barley β-glucan, CM-cellulose and, to a lesser extent, lichenan, but kinetic parameters indicate that it is primarily a xylanase. The products of hydrolysis of various xylans and xylopentaose differed for each enzyme and ranged from xylose to xyloheptaose depending on the substrate used. Each enzyme is endo-acting and has transferase as well as direct hydrolase activity. Inactivation byN-bromosuccinimide indicated the possible involvement of tryptophan in binding and/or catalysis.