Fructokinase

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Fructokinase (also known as ketohexokinase) is an enzyme that catalyzes the phosphorylation of fructose to produce fructose-1-phosphate. This reaction is the first step in the metabolism of dietary fructose in the liver, kidney, and intestine.

Function

Fructokinase plays a crucial role in the fructose metabolism pathway. It facilitates the conversion of fructose to fructose-1-phosphate by transferring a phosphate group from adenosine triphosphate (ATP) to fructose. This reaction is essential for the subsequent steps in the metabolism of fructose, leading to the production of intermediates that enter the glycolysis and gluconeogenesis pathways.

Isoforms

There are two main isoforms of fructokinase:

• KHK-C (Ketohexokinase-C) - Predominantly found in the liver.
• KHK-A (Ketohexokinase-A) - Found in various tissues including the kidney and intestine.

Clinical Significance

Mutations in the gene encoding fructokinase can lead to a condition known as essential fructosuria. This is a benign metabolic disorder characterized by the presence of fructose in the urine. Unlike other disorders of fructose metabolism, essential fructosuria does not cause significant health problems.

Pathway

The fructose metabolism pathway begins with the phosphorylation of fructose by fructokinase to form fructose-1-phosphate. This is followed by the action of aldolase B, which splits fructose-1-phosphate into dihydroxyacetone phosphate (DHAP) and glyceraldehyde. These intermediates can then enter the glycolytic pathway or be used in gluconeogenesis.

Regulation

Fructokinase activity is regulated by the availability of its substrate, fructose, and the levels of ATP. High levels of fructose can increase the activity of fructokinase, while low levels of ATP can inhibit its function.

See Also

• Fructose metabolism
• Glycolysis
• Gluconeogenesis
• Aldolase B
• Essential fructosuria