Dextransucrase: Acceptor substrate reactions

Studies were carried out on the acceptor specificity of dextransucrase which had been isolated from Streptococcus sanguis 10558. Radioactive acceptors were employed in reactions with cold sucrose and the counts incorporated were taken as a measure of “acceptor activity.” An order of relative activity was found to be polysaccharide > oligosaccharide > glycoside > monosaccharide. An evaluation of the time course of the reaction with α-methyl glucoside, or maltose, showed that a homologous series of oligosaccharides were formed from each. This suggested that the individual members of the series were related as precursors and products. The kinetics of the reaction with different acceptors was studied. All acceptors studied caused an activation of the enzyme and changes in the K_m for sucrose. The kinetic constants obtained were also used to compare the various acceptors.