Ketone body formation occurs as an alternative energy source during times of prolonged stress e.g. starvation. It occurs in the liver from an initial substrate of:
Then, three molecules of acetyl-CoA are effectively joined together in three enzyme steps sequentially catalyzed by:
Coenzyme A is regenerated and the ketone body acetoacetate is formed. Finally, acetoacetate is reduced to another ketone body, D-3-hydroxybutyrate, in a reaction catalyzed by 3-hydroxybutyrate dehydrogenase. This requires NADH. The oxidate state of the liver is such that the forward reaction is generally favoured; this results in more hydroxybutyrate being formed than acetoacetate.
Last reviewed 01/2018