Glycogenolysis
In glycogenolysis, glycogen stored in the liver and muscles, is converted first to
glucose-1- phosphate and then into glucose-6-phosphate. Two hormones which
control glycogenolysis are a peptide, glucagon from the pancreas and epinephrine
from the adrenal glands.
Glucagon is released from the pancreas in response to low blood glucose and
epinephrine is released in response to a threat or stress. Both hormones act upon
enzymes to stimulate glycogen phosphorylase to begin glycogenolysis and
inhibit glycogen synthetase (to stop glycogenesis).
Glycogen is a highly branched polymeric structure containing glucose as the
basic monomer. First individual glucose molecules are hydrolyzed from thechain, followed by the addition of a phosphate group at C-1. In the next step the
phosphate is moved to the C-6 position to give glucose 6-phosphate, a cross road
compound.
Glucose-6-phosphate is the first step of the glycolysis pathway if glycogen is the
carbohydrate source and further energy is needed. If energy is not immediately
needed, the glucose-6-phosphate is converted to glucose for distribution in the
blood to various cells such as brain cells.