BIOCHEMICAL CHARACTERISTICS OF 2 ENDO-BETA-1,4-XYLANASES PRODUCED BY PENICILLIUM-CAPSULATUM

Two endo-beta-1,4-xylan xylanohydrolases (EC 3.2-1.8), XynA and XynB, from solid-state cultures of Penicillium 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 28500, 5.0-5.2 (XynA) and 29500, 5.0-5.2 (XynB), respectively. Both enzymes are most active at pH 4 and 47-48-degrees-C, and have half-lives of 32 min (XynA) and 13 min (XynB) at pH 4, 60-degrees-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 beta-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 by N-bromosuccinimide indicated the possible involvement of tryptophan in binding and/or catalysis.