Mechanism of chain initiation by dextransucrase: Absence of terminal ‘sucrose’ linkage in newly synthesized dextran chains

Dextran was synthesized using dextransucrase from Streptococus sanguis 10558 and (F)-¹⁴C]sucrose as substrate to test the possibility that sucrose may be the initial acceptor for glucose. If sucrose is the initial acceptor, then dextran chains should have ¹⁴C] fructose in a terminal ‘sucrose’ linkage which can be cleaved under mild conditions. Although incorporation of ¹⁴C]fructose into dextran was observed, the label was not released by mild hydrolysis, indicating that sucrose is not the initiator for dextran synthesis. Incorporation of ¹⁴C]fructose into dextran might represent its ability to act as an acceptor, as suggested by the isolation of leucrose as a by-product in the reaction.