MONOSACCHARIDE ACCEPTOR SUBSTRATE-SPECIFICITY OF DEXTRANSUCRASE

The acceptor substrate specificity of dextransucrase from Streptococcus sanguis 10558 was examined utilizing analogs of methyl-α-d-glucopyranoside. The analogs include a series of α-methyl glycosides of several epimers, derivatives blocked at position 6, 6 blocked epimers, several β-methyl derivatives, and L-sugars. The products formed during reactions between the analogs, the enzyme and radiolabeled sucrose were separated by paper chromatography. This analysis permitted the simultaneous evaluation of transfer as well as polymerization reaction. All analogs examined served as acceptors with varying degrees of effectiveness. From the data obtained, a rough model for interaction of the enzyme with acceptors is proposed. Structural modifications at C2 and C4 produced the most significant alteration in the ability to serve as acceptors, and also inhibited the total catalytic activity of the enzyme. The enzyme is capable of using sugars in either 4C1 or 1C4 conformations. In addition, sugars blocked at C6, the normal site of glucose addition, can serve as good acceptors and therefore probably bind to the enzyme in a different orientation. The broad spectrum of analogs that can serve as acceptor suggests that the acceptor site has some flexibility. © 1991.