Joint Studies on Dextran-Producing and -Degrading Enzymes

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Dextransucrase, one of glucansucrases, catalyzes the formation of dextran from sucrose. Recently Dr. Kim has established a novel mutation technique, Vacuum UV radiation. The mutant strains obtained hyper-produced dextransucrase constitutively, giving a possibility to produce the large amount of dextran. Dextran and its oligosaccharides have been found to have several useful functions to human. In the international project we tried to elucidate the relationship between structures and functions of dextran-producing and -degrading enzymes, and prepared the dextran and isomaltooligosaccharides by both enzymes.(1) We succeeded in isolation of a hyper-produced dextransucrase gene and its expression in Escherichia coli. The mutated position was found in the promoter region. (2) A gene of isomaltotrio-dextranase was cloned and expressed in E. coli. The α-glucosidase gene was found in the upstream region of this gene. Both genes made a cluster structure, which was controlled by one promoter. (3) The large amount of dextran was prepared by hyper-produced dextransucrase. We examined the effective production method of pure isomaltotriose from dextran using isomaltotrio-dextranase. (4) An enzyme giving tetra- and penta-saccharides from dextran was purified and the properties were investigated. (5) Mechanism-based inactivator for dextranase was designed. Kinetic studies on inactivation indicated that compounds synthesized were found to be novel suicide substrate for dextranase.