A novel enzyme, trehalose synthase, was purified from a cell-free extract of Pimelobacter sp. R48 to an electrophoretically homogeneous state by successive chromatographies on DEAE-Toyopearl 650, Butyl-Toyopearl 650, and Mono Q HR5/5 columns. The molecular weight of the enzyme was estimated to be 62, 000 by SDS-polyacrylamide gel electrophoresis, and the enzyme had a pl of 4.6 by gel isoelectrofocusing. The enzyme catalyzed the lconversion of maltose into trehalose by intramoleculac transglucosylation. The enzyme also converted trehalose into maltose but was inactive on other saccharides. The N-terminal amino acid of the enzyme was serine. The optimum pH and temperature were pH 7.5 and 20°C, respectively. The enzyme was stable in the range of pH 6.0-9.0 and up to 30°C for 60 min. The rate of conversion of maltose into trehalose was independent of the maltose concentration. The maximum yield of trehalose from maltose were 81.8%, 80.9%, and 76.7% at 5, 15, and 25°C, respectively. The activity was inhibited by Cu²⁺, Hg²⁺, Ni²⁺, Zn²⁺, and Tris.

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