Acetoacetyl-CoA

Acetoacetyl-CoA is an important intermediate in the metabolic pathways of living organisms. It is formed from two molecules of acetyl-CoA by the action of the enzyme thiolase. Acetoacetyl-CoA can then be converted into hydroxymethylglutaryl-CoA (HMG-CoA) by the enzyme HMG-CoA synthase, a key step in the mevalonate pathway for the synthesis of sterols and other isoprenoids.

Structure and Properties

Acetoacetyl-CoA is a thioester that consists of a two-carbon acetyl group linked to a four-carbon acetoacetyl group via a coenzyme A molecule. The molecule has a molecular weight of approximately 853.2 g/mol. The acetoacetyl group is a ketone, which gives the molecule its characteristic reactivity.

Biosynthesis

The biosynthesis of acetoacetyl-CoA begins with the condensation of two molecules of acetyl-CoA, a reaction catalyzed by the enzyme thiolase. This results in the formation of acetoacetyl-CoA and a molecule of coenzyme A (CoA). The reaction is reversible, and in some organisms, the reverse reaction is used to generate acetyl-CoA from acetoacetyl-CoA.

Role in Metabolism

Acetoacetyl-CoA plays a central role in several metabolic pathways. In the mevalonate pathway, it is converted into HMG-CoA by the enzyme HMG-CoA synthase. This is a key step in the synthesis of sterols and other isoprenoids, which are vital components of cellular membranes and precursors of many other biologically important molecules.

In the ketogenesis pathway, acetoacetyl-CoA is converted into acetoacetate, a ketone body that can be used as an energy source by the brain and other tissues during periods of fasting or intense exercise.

Clinical Significance

Abnormalities in the metabolism of acetoacetyl-CoA can lead to a variety of health problems. For example, defects in the enzyme HMG-CoA synthase can result in HMG-CoA synthase deficiency, a rare genetic disorder that can cause episodes of hypoglycemia, metabolic acidosis, and coma.

File:Acetoacetyl-CoA.png

Structure of Acetoacetyl-CoA

See Also

• Acetyl-CoA
• Thiolase
• HMG-CoA synthase
• Mevalonate pathway
• Ketogenesis

References

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