Mechanism of sucrose conversion by the sucrose isomerase of Serratia plymuthica ATCC 15928

alpha-Glucosyltransferase was purified from Serratia plymuthica ATCC 15928. This enzyme was designated as a sucrose isomerase. its molecular weight wa s estimated at 65,000, the isoelectric point was 9.0, and the specific acti vity was 120 IU mg(-1). The K-m for sucrose was estimated at 65 mM. Glucose was demonstrated to be a competitive inhibitor. The purified sucrose isome rase was found to mediate sucrose conversion into several products: isomalt ulose, trehalulose, isomaltose, glucose, fructose, and isomelezitose. The m aximum conversion was obtained at pH 6.2 and 30 degrees C, but the product distribution was shown to depend on the reaction temperature. Addition of g lucose or fructose to the reaction mixture also modified this distribution. These observations allowed us to propose an explanation by a kinetic scheme combining an intra- and an intermolecular mechanism. (C) 1999 Elsevier Sci ence Inc.