UDP-glucose 4-epimerase

UDP-glucose 4-epimerase

UDP-glucose 4-epimerase is an enzyme that plays a crucial role in the metabolism of galactose. It catalyzes the reversible conversion of UDP-glucose to UDP-galactose, a key step in the Leloir pathway of galactose metabolism. This enzyme is encoded by the GALE gene in humans.

Structure

UDP-glucose 4-epimerase is a homodimeric enzyme, meaning it consists of two identical subunits. Each subunit binds a molecule of NAD+, which is essential for its catalytic activity. The enzyme's active site is where the epimerization reaction occurs, involving the transient reduction of the sugar moiety by NAD+.

File:Human GALE bound to NADH and UDP-glucose.png

Structure of human GALE bound to NADH and UDP-glucose.

Function

The primary function of UDP-glucose 4-epimerase is to interconvert UDP-glucose and UDP-galactose. This reaction is vital for the proper utilization of galactose obtained from the diet. In the Leloir pathway, galactose is first phosphorylated to galactose-1-phosphate, which is then converted to UDP-galactose. UDP-glucose 4-epimerase facilitates the conversion of UDP-galactose to UDP-glucose, which can then enter glycolysis or be used in the synthesis of glycogen and other glycoproteins.

File:Leloir pathway.png

Diagram of the Leloir pathway of galactose metabolism.

Clinical significance

Mutations in the GALE gene can lead to a condition known as epimerase-deficiency galactosemia. This disorder is characterized by an inability to properly metabolize galactose, leading to the accumulation of toxic substances in the body. Symptoms can include jaundice, hepatomegaly, and cataracts. The severity of the condition can vary, with some individuals experiencing mild symptoms and others having more severe manifestations.

Related enzymes

UDP-glucose 4-epimerase is part of a family of enzymes known as epimerases, which catalyze the inversion of stereochemistry at specific carbon atoms in sugar molecules. Other related enzymes include UDP-glucuronate 4-epimerase and UDP-N-acetylglucosamine 4-epimerase.

Related pages

• Galactosemia
• Leloir pathway
• NAD+
• Metabolism