Glycogen metabolism The metabolic path for Glycogen starts with alfa-D-Glucose that isphosphorylated by a set of enzymes: Hexokinase 1 ( HXK1 ) , , , Hexokinase 2 ( HXK2 ) , ,, Hexokinase 3 ( HXK3 ) , , , Glucokinase (hexokinase 4) ( HXK4 ) , ,, ,  andalpha-(D)-Glucose-6-phosphate is formed. Also, alpha-D-Glucose isisomerically transformed into beta-D-Glucose by Galactose mutarotase (aldose1-epimerase) ( GALM ) , , . Beta-D-Glucose undergoes the same transformations that alpha-D-glucose underthe action of the same enzymes to form beta-(D)-Glucose-6-phosphate whichsubsequently takes another stereoisomerisation step toalpha-(D)-Glucose-6-phosphate. This step is catalyzed by Glucose phosphateisomerase ( GPI ) . Phosphoglucomutase 1 ( PGMU ) catalyzesthe next isomerization of alpha-(D)-Glucose-6-phosphate leading to formation ofalpha-(D)-Glucose 1-phosphate , . UDP isthen attached to alpha-(D)-Glucose 1-phosphate by UDP-glucose pyrophosphorylase 1( UGPA1 ) or UDP-glucose pyrophosphorylase 2 ( UGPA2 ) to formUDP-D-glucose , , , . UDP-D-glucose polymerizes with (alpha-D-glucosyl-(1-4))n to formGlycogen. This step is catalyzed by Glucan (1,4-alpha-), branching enzyme 1 (GLGB ) , , , . Onthe other hand, Glycogen synthase 1 (muscle) ( GYS1 ) and Glycogen synthase 2(liver) ( GYS2 ) can cleave UDP-D-glucose from Glycogen to release(alpha-D-glucosyl-(1-4))n , , ,, . A number of glycogen phosphorylases (Phosphorylase,glycogen, liver ( PYGL ), Phosphorylase, glycogen, brain ( PYGB ) andPhosphorylase, glycogen, muscle ( PYGM )) mediate phosphorolysis ofGlycogen, which is regarded as transfer of one sugar residue (alpha-D-glucose1-phosphate) from Glycogen to inorganic phosphate. As a result Glycogenchain decreased for one sugar moiety with formation of a reduced product(alpha-D-glucosyl-(1-4))(,n=3)-alpha-D-glucosyl-(1-6)*(glycogen). , , , , , . Thisproduct is a substrate for Amylo-1, 6-glucosidase, 4-alpha-glucanotransferase - glycogendebranching enzyme ( GDE ) that fractionates the polymeric structure to form twometabolites: the main chain - alpha-D-glucosyl-(1-6)*(glycogen) and branch chainof Glycogen - (alpha-D-glucosyl-(1-4))(,n=3) , ,, , . GDE also affects both productsof the latter reaction. Alpha-D-glucosyl-(1-4))(,n=3) can be directlyrepolymerized to Glycogen; alpha-D-glucosyl-(1-6)*(glycogen) can befurther hydrolyzed giving alpha-D-Glucose as a product., , .