Dextran acceptor reaction of Streptococcus sobrinus glucosyltransferase GTF-I as revealed by using uniformly 13C-labeled sucrose Original Research Article

A sucrose glucosyltransferase GTF-I from cariogenic Streptococcus sobrinus transferred the uniformly 13C-labeled glucosyl residue ([U-13C]Glc) from [U-13C]sucrose to exogenous dextran T500 at the non-reducing-end, mostly by α-(1→6) linkages and partially by α-(1→3) linkages, as revealed by the 13C–13C NMR coupling pattern. With increasing amounts of [U-13C]sucrose, transfer of [U-13C]Glc to the α-(1→3)-linked chain became predominant without increase in the number of chains. The transfer of [U-13C]Glc to an isomaltopentaose acceptor occurred similarly to its transfer to T500. α-(1→3)-branches in the [U-13C]dextran, specifically synthesized from [U-13C]sucrose by a Streptococcus bovis dextransucrase, were not formed by GTF-I, as judged by the observation that a newly-formed α-1,3,6-banched [U-13C]Glc was not detected, which could have been formed by transferring the unlabeled Glc from sucrose to the internal α-(1→6)-linked [U-13C]Glc at C-3. The 13C–13C one-bond coupling constants (1J) were also recorded for the C-1C-6 bond of the internal α-(1→6)-linked [U-13C]Glc and of the non-reducing-end [U-13C]Glc.