Purification and properties of xylan-degrading enzyme from Aspergillus terreus 603

Abstract

The general properties of the crude lyophilized xylan-degrading enzyme produced by Aspergillus terreus 603 in surface culture were studied. An enzyme: substrate ratio of 1:4:6 was the most appropriate, under the assay conditions used, without considerable product inhibition. Maximal enzyme activity was reached on using 18·8 mg hemicellulose B in the reaction mixture at pH 4·99 and 55°C. The enzyme was isolated from a filtrate of a static culture with various agents. The fraction precipitated at 66·6% ethanol possessed the highest recovered activity. Purification of partially purified enzyme was attempted by Sephadex G-150 column chromatography and afforded three protein components. The first component was the major and possessed almost all of the recovered xylan-degrading activity. The most active fraction of this component showed 32-fold purification and effected 79·2% saccharification of xylan in 10 min at 55°C, with maximal activity at 45°C and pH 4·99. Thermal treatment of the enzyme at pH 3·42 had the most adverse effect on enzyme activity. Calcium ions slightly activated the enzyme. Co 2+, Mn 2+, Fe 3+ ions, PCMB or cysteine-HCl partially inhibited the enzyme. Reduced glutathione and cystine had smaller inhibitory effects, while iodine at a final concentration of 10 −3 M completely inhibited the enzyme.