1 INTRODUCTION
Sucrose synthase (SuSy, EC
2.4.1.13) belongs to the glycosyltransferase-4 subfamily (GT-4), which
can catalyze the reversible reaction of sucrose synthesis and
cleavage.[1] A large number of studies have shown
that the activity of SuSy depended on pH value.[2,
3] At pH 7.5–9.5, it displays optimal activity in the direction of
sucrose synthesis, while acidic pH promotes the reverse reaction and
decomposes sucrose at pH 5.5–7.5 to produce nucleoside diphosphate
(NDP) glucose and fructose. Recently, using sucrose to recover the
“donor” uridine 5’-diphosphate (UDP) glucose (UDPG) by combining SuSy
with Leloir GT (SuSy-GT) has aroused considerable interest in the
development of biocatalytic glycosylation process, because the
glycosylation of most known conjugates by Leloir GT requires the
participation of UDPG.[4-6] In the SuSy-GT cascade
reaction (Scheme 1), a UDP cycle is created using sucrose and SuSy which
makes UDPG continuously regenerated as an expedient donor for glucoside
production, which is the shortest, and probably the most appealing one
among the three routes involving synthase, phosphorylase, and kinase for
UDPG synthesis.[7]