Purification, characterization and substrate specificities of xylanase isoenzymes from Melanocarpus albomyces IIS 68.

Abstract

The ascomycetous fungus Melanocarpus albomyces when grown on wheat straw produced seven extracellular xylanase isoenzymes, designated as la, Ib, Ic, IIa, lib, llc, and lId. All seven xylanases were purified to homogeneity by gel filtration and ion-exchange chromatography. The molecular mass (kDa) of la, lb, Ic, Ila, lIb, lIc, and lId were estimated to be 22.9, 20.7, 18.6, 31.3, 25.4, 38.5, and 34.3, respectively by SDS-PAGE, and 23.7, 20.5, 17.1, 31.7, 25.1, 39.8, and 32.2, respectively by gel filtration. The isoelectric points of Ia, lb, Ic, Ila and IIb were found to be 6.2, 6.3, 6.4, 3.7, and 4.4, respectively. The activity of the isoenzymes was dependent on the type of the xylan substrates; Xylanases Ia, lb, and Ic showed highest specific activity toward larchwood xylan (an arabinoglucuronoxylan), IIa and Ilc toward birchwood xylan (a glucuronoxylan), and llb and IId toward beechwood xylan (a glucuronoxylan). Four isoenzymes la, lb, Ic, and Ila had an arabinose-releasing property on larchwood xylan. Application of specific isoenzymes as prebleaching agents in paper manufacture is proposed.