Biochemical properties of a putative thermostable dextranase gene from Thermotoga lettingae TMO were determined in a recombinant protein (TLDex) expressed in Escherichia coli and purified to sevenfold apparent homogeneity. The 64-kDa protein displayed maximum activity at pH 4.3, and enzyme activity was stable from pH 4.3-10. The optimal temperature was 55-60 degrees C during 15 min incubation, and the half-life of the enzyme was 1.5 h at 65 degrees C. The enzyme showed higher activity against alpha-(1 --> 6) glucan and released isomaltose and isomaltotriose as main products from dextran T2000. An unusual kinetic feature of TLDex was the negative cooperative behavior on the reaction of dextran T2000 cleavage. Enzyme activity was not significantly affected by the presence of metal ions, except for the strong inhibited by 1 mM Fe(2+) and Ag(2+). TLDex may prove useful as an enzyme for high temperature sugar milling processes.
