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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.

A multiactivity preparation was isolated from solid-state cultures of Penicillium capsulatum. It migrated as a single band (pI 4.02) on isoelectric focusing, on nondenaturing polyacrylamide gradient gel electrophoresis (Mr 242,500), and on SDS-polyacrylamide gradient gel electrophoresis (Mr 135,000). It also migrated as a single band when pretreated with 6 M urea (or 6 M guanidine-HCl) plus octyl glucoside and electrophoresed in the presence of urea. Thus, the purified entity is a dimer of similar, if not identical, subunits. Transmission electron microscopy of negatively stained preparations revealed bipartite projections with length to width ratios of 2:1 and obvious division into two main masses. Each of the latter exhibited three smaller submasses. The calculated molecular weights of the native particle and subunits were consistent with the values obtained by electrophoresis. The purified preparation catalysed the hydrolysis of p- nitrophenyl -β- D - glucoside , p- nitrophenyl -β- D - xyloside , cellobiose, laminarin, β-glucan, lichenan, and carboxyl reduced pneumococcal type III polysaccharide. We conclude that each subunit is composed of three enzymes: β-glucosidase, laminarinase, and lichenase. However, the possibility that each subunit is a single protein with three domains, each displaying one of the above activities, is not precluded. Glucose accumulated during the hydrolysis of β-glucan (or laminarin), but oligomeric intermediates did not. This would imply exoaction. By contrast, the rate of reduction in viscosity of a solution of the β-glucan greatly exceeded the rate of release of reducing sugars therefrom. This is typical of endoaction. We reconcile this apparent contradiction by proposing that the products of the endoacting β-glucanase and laminarinase components are immediately acted upon by the exoacting β-glucosidase component to yield glucose, with obvious advantages to the cell. Complexes with the ability to effect complete conversion of polymers to monomers should also have considerable commercial potential.