Glycogen phosphorylase longer cause the phosphorylation cascade that ends with formation of (active) glycogen phosphorylase a. These modifications initiated by insulin end glycogenolysis in order to preserve what glycogen stores are left in the cell and trigger glycogenesis (rebuilding of glycogen). Phosphorylase a and phosphorylase b each exist in two forms a T (tense) inactive state and R (relaxed) state. Phosphorylase b is normally in the T state, inactive due to the physiological presence of ATP and Glucose 6 phosphate, and Phosphorylase a is normally in the R state (active). An isoenzyme of glycogen phosphorylase exists in the liver sensitive to glucose
Glycogen synthase glycogen synthase is highly conserved among species, glycogen synthase likely forms a tetramer in humans as well. Glycogen synthase can be classified in two general protein families. The first family (GT3), which is from mammals and yeast, is approximately 80 kDa, uses UDP-glucose as a sugar donor, and is regulated by phosphorylation and ligand binding. The second family (GT5), which is from bacteria and plants, is approximately 50 kDA, uses ADP-glucose as a sugar donor, and is unregulated. Although the catalytic mechanisms used by glycogen synthase are not well known, structural similarities to glycogen phosphorylase at the catalytic and substrate