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An isomaltotriose-producing endo-dextranase was simply purified from cell-free culture broth of a Fusarium sp. by ethanol fractionation and consecutive column chromatographibs 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 enzyme was estimated to be about 69 kDa by SDS-PAGE. The enzyme is an acidic protein with a pI of 4.6. The optimum pH and temperature were pH 6.5 and 35℃, respectively. The enzyme was completely stable over the range of pH 4.5-11.8 at 4 for 24 h and at temperatures below 45℃. Inactivation of the enzyme was found to be partial with 5 mM Cu^<2+>, being about 70% inhibition and complete with 5 mM of Fe^<3+> Hg^<2+>, Ag^+ or NBS. The enzyme split dextran in an endo-lytic action to produce a large amount of isomaltotriose and a slight amount of isomaltose rind glucose. The anomeric configurations of the reaction products formed by the enzyme were α-form, indicating that the α-glycoside linkages in the substrate are retained. The final yield of isomaltotriose from dextran T-2000 was about 62%.