OrganismsOrganisms generally store branched α-glucan as the
reserve polysaccharides. The α-1,6-glucosidic bonds of
α-glucan link numerous α-1,4-linear chains to form
macromolecules called glycogen in animals and bacteria or
amylopectin in plants. The α-1,6-glucosidic linkages are
formed by glycogen branching enzyme and starch branching
enzyme (BE), and therefore BE plays a very important part
in the synthesis of the distinct fine structure of glycogen and
amylopectin. Although glycogen-synthesizing organisms
such as animals and bacteria have usually only one type of
BE, green plants are known to have two types of BE, BEI
and BEII, having distinct structure and enzymatic properties.
1‒6)(1‒6) It is also known that BEII is further differentiated
into BEIIa and BEIIb isoforms in cereals, although BEIIb is
usually specifically expressed in endosperm while BEIIa is
ubiquitously present in every tissue.