X. Synthesis and Utilization of Ketone Bodies
Ketone bodies are utilized exclusively by extrahepatic tissues; heart
and skeletal muscle use them particularly effectively.
- If the ketone is beta-hydroxybutyrate, the first step must be
reoxidation to acetoacetate, in a reversal of the reaction described previously.
- Acetoacetate is activated by transfer of CoA from succinyl CoA.
Acetoacetate is activated by transfer of CoA from succinyl CoA in a
reaction catalyzed by succinyl CoA: 3-ketoacid CoA transferase.
- The enzyme catalyzing this reaction is absent from liver; hence
liver, which synthesizes ketone bodies, cannot use them. This
places liver in the role of being a net producer of ketones.
- The resulting acetoacetyl CoA can be cleaved by thiolase to form two molecules of acetyl CoA, which can then be oxidized by the tricarboxylic acid cycle.