Biology Reference
In-Depth Information
OH
OH
O
O
+inorganic phosphate
HO
HO
HO
HO
O
O
OH
OH
O
P
O
nonreducing end
O
glycose 1-phosphate
Figure 3.1
Typical phosphorolytic reaction catalyzed by phosphorylase.
to
produce
the
corresponding
glycose
1-phosphates
and
monosaccharides.
-Glucan and cellodextrin phosphorylases have
been used in various investigations for the practical synthesis of
poly- or oligosaccharides with relatively higher DPs, as well as the
related poly- and oligosaccharide-based materials. Although it has
been reported that some phosphorylases, such as
α
-1,3-oligoglucan
and kojibiose phosphorylases, recognize glucans with higher DPs
and catalyze their phosphorolysis, there have not been many studies
on the synthesis of poly- or oligosaccharides catalyzed by these
enzymes.
β
3.2
Outlines of Phosphorylase Catalyses
Of
-glucan phosphorylase (glycogen
phosphorylase, starch phosphorylase, hereafter, this enzyme is
simply called “phosphorylase” in this topic) is the most extensively
studied and is found in animals, plants, and microorganisms [3]. The
role of phosphorylase is considered to be in utilization of storage
polysaccharides in the glycolytic pathway. This enzyme catalyzes the
reversible phosphorolysis of
the
phosphorylases,
α
4)-glucans at the nonreducing
end, such as glycogen and starch, in the presence of inorganic
phosphate, giving rise to
α
-(1
→
-
d
-glucose 1-phosphate (Glc-1-P) (Fig.
3.2). The reaction mechanism of phosphorylase is a rapid equilibrium
random bi bi mechanism [4]. In animal muscle, phosphorylases
are regulated by a phosphorylation/dephosphorylation system
comprising a phosphorylase kinase and a phosphorylase phosphatase
[5,6]. The phosphororylated and dephosphororylated forms are
denoted as phosphorylase
α
, respectively;
the latter has a requirement for adenosine 5'-monophosphate to
display activity. In contrast, phosphorylases isolated from plants and
microorganisms are not regulated by this system.
a
and phosphorylase
b
