PURIFICATION AND CHARACTERIZATION OF 2 LOW-MOLECULAR-MASS ALKALINE XYLANASES FROM FUSARIUM-OXYSPORUM F3

Two low molecular mass endo-1,4-P-D-xylanases from Fusarium oxysporum were purified to homogeneity by gel-filtration and ion-exchange chroma tography. They exhibit molecular masses of 20.8 (xylanase I) and 23.5 (xylanase II) kDa, and isoelectric points of 9.5 and 8.45-8.70, respec tively. Both xylanases display remarkable pH (9.0) stability. At 40 to 55 degrees C xylanase II is more thermostable than xylanase I but les s active on xylan. In contrast to xylanase I, xylanase II is able to h ydrolyze eryl-(beta-D-glucopyranosyl)-beta-D-xylopyranoside (muxg). Ne ither of these enzymes hydrolyze xylotriose. They bind on crystalline cellulose but not on insoluble xylan. Analysis of reaction mixtures by high pressure liquid chromatography revealed that both enzymes cleave preferentially the internal glycosidic bonds of xylopentaose and oat spelts xylan. Thus the purified enzymes appeared to be true endo-beta- 1,4-xylanases. The amino terminal sequences of xylanases I and II show no homology. Xylanase I shows high similarity with alkaline low molec ular mass xylanases of family G/11.