ch> ck> ckx5><x x x >o o o o
Catabolism of a small glycogen molecule by glycogen phosphorylase and debranching enzyme. P; = inorganic
phosphate; G-l-P = glucose-1-phosphate.
glycogenin and up to 60,000 glucosyl units
In the liver, 20-40 ^-particles are aggregated into rosettes,
known as (a-particles).
Glycogenolysis is catalyzed by two enzymes unique to
the pathway: glycogen phosphorylase and debranching en-
zyme. The former normally regulates the rate of glucose
release from glycogen. The progressive degradation of
glycogen is illustrated in Figure 15-8. Glycogen phospho-
rylase catalyzes the release of glucose-
the terminal residue of a nonreducing end of a glyco-
gen branch, by means of phosphorolysis. A molecule of
inorganic phosphate attacks the Ci side of an
4) glycosidic bond, leaving a hydroxyl group on C
that remains in the glycogen polymer. The reaction is
analogous to hydrolysis, in which water attacks and
cleaves bonds. The phosphorolysis reaction is summarized
(Glucose)« + P j ^ (glucose)«_i + glucose-1-Phosphate
The energy stored in the a (1 —> 4) glycosidic bond during
the condensation reaction in glycogen synthesis is suffi-
cient to permit the formation of a glucose-phosphate bond
without using ATP.