Pathway maps

Glycogen metabolism
Glycogen metabolism

Object List (links open in MetaCore):, GPI, alpha-D-glucosyl- (1-6)*(glycogen), alpha-(D)-Glucose 1-phosphate,, UGPA1, GALM, alpha-D-glucosyl-(1-4)-beta-D-glucose cytoplasm, GYS1, PYGB,, HXK4, PYGM, HXK2, alfa-D-Glucose, (alpha-D-glucosyl- (1-4))(,n=3),,, Glycogen, UDP-D-glucose, PGMU, alpha-(D)-Glucose- 6-phosphate, GDE, GYS2, UGPA2, HXK3, beta-D-Glucose, beta-(D)-Glucose- 6-phosphate,,,, HXK1, PYGL, (alpha-D-glucosyl- (1-4))(,n=3)-alpha- D-glucosyl- (1-6)*(glycogen),,,, GLGB,


Glycogen metabolism

The metabolic path for Glycogen starts with alfa-D-Glucose that is phosphorylated by a set of enzymes: Hexokinase 1 ( HXK1 ) [1], [2], [3], Hexokinase 2 ( HXK2 ) [4], [5], [6], Hexokinase 3 ( HXK3 ) [7], [6], [8], Glucokinase (hexokinase 4) ( HXK4 ) [9], [10], [11], [12], [13] and alpha-(D)-Glucose-6-phosphate is formed. Also, alpha-D-Glucose is isomerically transformed into beta-D-Glucose by Galactose mutarotase (aldose 1-epimerase) ( GALM ) [14], [15], [16]. B eta-D-Glucose undergoes the same transformations that alpha-D-glucose under the action of the same enzymes to form beta-(D)-Glucose-6-phosphate which subsequently takes another stereoisomerisation step to alpha-(D)-Glucose-6-phosphate. This step is catalyzed by Glucose phosphate isomerase ( GPI ) [17]. Phosphoglucomutase 1 ( PGMU ) catalyzes the next isomerization of alpha-(D)-Glucose-6-phosphate leading to formation of alpha-(D)-Glucose 1-phosphate [18], [19]. UDP is then attached to alpha-(D)-Glucose 1-phosphate by UDP-glucose pyrophosphorylase 1 ( UGPA1 ) or UDP-glucose pyrophosphorylase 2 ( UGPA2 ) to form UDP-D-glucose [20], [21], [22], [23].

UDP-D-glucose polymerizes with (alpha-D-glucosyl-(1-4))n to form Glycogen. This step is catalyzed by Glucan (1,4-alpha-), branching enzyme 1 ( GLGB ) [24], [25], [26], [27]. On the 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 [28], [29], [30], [31], [32]. A number of glycogen phosphorylases (Phosphorylase, glycogen, liver ( PYGL ), Phosphorylase, glycogen, brain ( PYGB ) and Phosphorylase, glycogen, muscle ( PYGM )) mediate phosphorolysis of Glycogen, which is regarded as transfer of one sugar residue (alpha-D-glucose 1-phosphate) from Glycogen to inorganic phosphate. As a result Glycogen chain decreased for one sugar moiety with formation of a reduced product (alpha-D-glucosyl-(1-4))(,n=3)-alpha-D-glucosyl-(1-6)*(glycogen). [33], [34], [35], [36], [37], [38]. This product is a substrate for Amylo-1, 6-glucosidase, 4-alpha-glucanotransferase - glycogen debranching enzyme ( GDE ) that fractionates the polymeric structure to form two metabolites: the main chain - alpha-D-glucosyl-(1-6)*(glycogen) and branch chain of Glycogen - (alpha-D-glucosyl-(1-4))(,n=3) [39], [40], [41], [42], [43]. GDE also affects both products of the latter reaction. Alpha-D-glucosyl-(1-4))(,n=3) can be directly repolymerized to Glycogen; alpha-D-glucosyl-(1-6)*(glycogen) can be further hydrolyzed giving alpha-D-Glucose as a product. [40], [41], [43].


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