PURIFICATION AND CHARACTERIZATION OF AN ISOMALTOTRIOSE-PRODUCING ENDO-DEXTRANASE FROM A FUSARIUM SP

An isomaltotriose-producing endo-dextranase was simply purified from c ell-free culture broth of a Fusarium sp. by ethanol fractionation and consecutive column chromatographies using DEAE-Toyopearl and Bio-Gel P -100. The purified enzyme was judged to be homogeneous on PAGE and SDS -PAGE as well as isoelectric focusing. The molecular mass of the enzym e was estimated to be about 69 kDa by SDS-PAGE. The enzyme is an acidi c protein with a pI of 4.6. The optimum pH and temperature were pH 6.5 and 35 degrees C, respectively. The enzyme was completely stable over the range of pH 4.5-11.8 at 4 degrees C for 24 h and at temperatures below 45 degrees C. Inactivation of the enzyme was found to be partial with 5 mM Cu2+, being about 70% inhibition and complete with 5 mM of Fe3+, Hg2+, Ag+ or NBS. The enzyme split dextran in an endo-lytic acti on to produce a large amount of isomaltotriose and a slight amount of isomaltose and glucose. The anomeric configurations of the reaction pr oducts formed by the enzyme were alpha-form, indicating that the alpha -glycoside linkages in the substrate are retained. The final yield of isomaltotriose from dextran T-2000 was about 62%.