PURIFICATION AND PROPERTIES OF THE XYLANASE PRODUCED BY THERMOMYCES-LANUGINOSUS

Xylanase obtained by the submersed fermentation of Thermomyces lanugin osus, a strain classified in the German type culture collection under the number DSM 5826, was purified to homogeneity by a combination of c hromatographic methods and characterized. The molecular mass of the en zyme was estimated by SDS-electrophoresis, gradient gel electrophoresi s, or gel filtration at 25.5 kDa, 24.0 kDa, or 22.5 KDa, respectively. The isoelectric point of the enzyme was determined to be pH 4.1. It w as found that the enzyme hydrolyzed xylan as an endoxylanase and had p ractically no cellulolytic or any other similar hydrolytic activity. I t exhibited the highest activity at a pH around 7.0 and in the tempera ture range of 60-70 degrees C, It was found that the enzyme contains o nly one cysteine residue which was important for the xylanase activity , since dithiobis-2-nitrobenzoic acid, p-hydroxymercuribenzoic acid, a nd Hg2+ ions completely inhibited the enzyme. Mn2+, Fe2+, and beta-mer captoethanol enhanced the xylanase activity; the best results were obt ained by the combined action of Fe2+ ions and beta-mercaptoethanol. Xy lanase was stable for 96 h at a pH between 5.0-9.0 and at temperatures up to 60 degrees C. Significant stabilization of the enzyme was achie ved by the addition of glycerol, beta-mercaptoethanol, or polyethylene glycol.