UTP—glucose-1-phosphate uridylyltransferase

Crystal structure of UTP-glucose-1-phosphate uridylyltransferase from Burkholderia xenovorans

Human UDP-glucose pyrophosphorylase isoform 1 subunit in complex with UDP-glucose

UTP—glucose-1-phosphate uridylyltransferase mechanism

UTP—glucose-1-phosphate uridylyltransferase (EC 2.7.7.9) is an enzyme that catalyzes the biochemical reaction involving the transfer of a uridine triphosphate (UTP) molecule to glucose-1-phosphate, resulting in the formation of uridine diphosphate glucose (UDP-glucose) and pyrophosphate. This enzyme plays a crucial role in carbohydrate metabolism and glycogen biosynthesis, serving as a key regulatory point in the conversion of glucose to glycogen. UDP-glucose acts as a glucose donor in various biosynthetic processes, including the synthesis of glycogen, glycoproteins, and glycolipids.

Function

UTP—glucose-1-phosphate uridylyltransferase is essential for the synthesis of glycogen from glucose. By converting glucose-1-phosphate to UDP-glucose, it provides the activated form of glucose required for the elongation of the glycogen molecule. This enzyme is particularly important in liver and muscle tissues where glycogen storage is critical for maintaining glucose homeostasis during fasting and physical activity.

Mechanism

The enzyme catalyzes the reaction in two steps:

1. UTP and glucose-1-phosphate bind to the enzyme, forming a complex.
2. The enzyme then mediates the transfer of UTP to glucose-1-phosphate, producing UDP-glucose and releasing pyrophosphate.

The reaction is energetically favorable due to the subsequent hydrolysis of pyrophosphate by pyrophosphatase into two inorganic phosphate molecules, which drives the reaction forward.

Clinical Significance

Mutations in the gene encoding UTP—glucose-1-phosphate uridylyltransferase can lead to metabolic disorders such as Glycogen storage disease type I (GSD I), also known as von Gierke's disease. This condition is characterized by an accumulation of glycogen and fat in the liver and kidneys, leading to hepatomegaly, hypoglycemia, and lactic acidosis. Early diagnosis and management are crucial for preventing severe complications.

Genetic Regulation

The expression of the gene encoding this enzyme is tightly regulated by hormonal and nutritional signals. Insulin and glucagon play significant roles in the upregulation and downregulation of this enzyme, respectively, in response to blood glucose levels. This regulation ensures that glycogen synthesis occurs primarily when glucose is abundant, and energy storage is needed.

See Also

• Glycogen synthase
• Glycogen phosphorylase
• Carbohydrate metabolism
• Glycogen storage disease