ABSTRACT
CGTase produces CDs by intramolecular transglycosylation (cyclization reaction), where the enzyme cleaves the
α
-1,4-linkage of the substrates in an endo manner and transfers the newly produced reducing end to the nonreducing end of its own molecule (Figure 22.1). CGTase also catalyzes two intermolecular transglycosylation reactions called
coupling
and
disproportionation
. In coupling, the enzyme utilizes CDs as glycosyl donors, where the CD ring is opened and the resulting reducing end is transferred to a linear maltooligosaccharide or some other acceptor molecule to form a linear product. Disproportionation is a transfer reaction between two maltooligosaccharide molecules to yield linear oligosaccharides with various degrees of polymerization. In the presence of suitable acceptors such as glucose and sucrose, the enzyme also transfers the glycosyl residues produced from glucans to the acceptors. In addition to these transglycosylations,
CGTase exhibits a weak hydrolysis activity on starch and CDs, which is possibly understood as the transfer of the glycosyl residue to a water molecule. CGTase possesses extreme industrial usefulness because of the various products, CDs, other linear oligosaccharides and glycosides, which are diversely and increasingly applied to food, pharmaceutical, and cosmetic industries.
