Biology Reference
In-Depth Information
phosphorylase (EC 2.4.1.97) [25-27]. These three enzymes have
been found as intracellular enzymes in algae and euglenida cells.
β
-1,3-Oligoglucan and laminaribiose phosphorylases are found
in
and catalyze the reversible phosphorolysis of
laminaribiose and its trimer, and also higher oligomers. Inversion of
the anomeric configuration occurs with these enzymes, giving rise
to Glc-1-P. The key difference in the reactions catalyzed by these two
enzymes is that
Euglea gracilis
-1,3-oligoglucan phosphorylase phosphorolyzes
laminaritriose faster than lamianribiose and vise versa for
lamiaribiose phosphorylase. A mixture of laminarioligosaccharides
with varying DPs was synthesized from glucose and Glc-1-P by the
combined actions of these two enzymes [28]. In contrast to these
two enzymes, laminarin phosphorylase phosphorolyzes a polymeric
substrate.
β
β
-acetylhexosamine phosphorylase catalyzes
the phosphorolysis of Gal-
-1,3-Galactosyl-
N
3)-GalNAc
oligosaccharides [30]. In the reverse reaction, this enzyme specifically
recognizes
β
-(1
→
3)-GlcNAc or Gal-
β
-(1
→
-galactose 1-phosphate as a donor and GlcNAc and
GalNAc as acceptors. Chitobiose phosphorylase phosphorolyzes the
conversion of
α
N,N'
-diacetylchitobiose into
α
-GlcNAc 1-phosphate
and GlcNAc [30].
3.3
Phosphorylase-Catalyzed Glycosylation
As mentioned earlier, phosphorylase catalyzes the reversible
phosphorolytic reaction of
4)-glucans at the nonreducing end
in the presence of inorganic phosphate, giving Glc-1-P (Fig. 3.2) [1].
By means of reversibility of the reaction,
α
-(1
→
4)-glycosidic linkage
can be constructed by the phosphorylase-catalyzed glycosylation
using Glc-1-P as a glycosyl donor [31]. As a glycosyl acceptor in
the glycosylation reaction, maltooligosaccharides with DPs higher
than the smallest one, which is recognized by phosphorylase, are
used. The glycosyl acceptor is often called a “primer.” The smallest
glycosyl acceptor for the phosphorylase-catalyzed glycosylation is
typically maltotetraose (Glc
α
-(1
→
), whereas that for the phosphorolysis
4
is maltopentaose (Glc
). In the glycosylation, a glucose unit is
transferred from Glc-1-P to a nonreducing end of the primer to form
α
5
-(1
→
4)-glycosidic linkage. When the excess molar ratio of Glc-
