Glycogenesis

Source: https://bio.libretexts.org/Bookshelves/Biochemistry/Fundamentals_of_Biochemistry_(Jakubowski_and_Flatt)/02%3A_Unit_II-_Bioenergetics_and_Metabolism/15%3A_Glucose_Glycogen_and_Their_Metabolic_Regulation/15.02%3A_Glycogenesis

Step 1: Glucose 6-phosphate is converted to […]

glucose 1-phosphate

The isomerization of glucose 6-phosphate to glucose 1-phosphate is catalyzed by […]

phosphoglucomutase

Step 2: Glucose-1-phosphate is then “activated” by the attachment of a uridine diphosphate group, which produces […]

UDP-glucose or uracil diphosphate glucose

The production of UDP-glucose is catalyzed by […]

UTP-glucose-1-phosphate uridylyltransferase (preferred name)

Also called:

• UDP-glucose pyrophosphorylase

• UGPase

• uridyltransferase

Step 3: UDP-glucose is used enzyme […] to extend the main glycogen chain.

glycogen synthase (GS or GYS)

• UDP serves as a good leaving group, allowing the formation of the alpha-1,4 bond.

Glycogen synthase requires a glycogen primer of 4 to 6 glucose residues to add new residues to the main chain. The small docking protein, […], provides this primer.

glycogenin (GN or GYG)

Step 4: The branching of glycogen chains is carried out by the enzyme […].

glycogen branching enzyme (GBE)

Glycogen branching enzyme (GBE) catalyzes the hydrolytic cleavage of a(n) […] and subsequent inter- or intra-chain transfer of the fragment to the […] position of an alpha-glucan.

alpha-1,4 glycosidic linkage; C6 hydroxyl

• An alpha-glucan is a polysaccharide made of glucose units linked by alpha bonds.

• In this image, an inter-chain transfer is occurring.

• Above the arrow, the GBE enzyme removes several glucose residues (usually around 7) from one linear glycogen chain and then attaches it as an alpha-1,6 branch to the other chain.

Glycogen branching creates additional […], which can act as a primer site for […] (the main enzyme that breaks down glycogen).

non-reducing ends; glycogen phosphorylase

• Because of this, glucose residues can be released very quickly when needed.