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Ketone bodies are water-soluble molecules or compounds that contain the ketone groups produced from fatty acids by the liver (ketogenesis). [1] [2] Ketone bodies are readily transported into tissues outside the liver, where they are converted into acetyl-CoA (acetyl-Coenzyme A) – which then enters the citric acid cycle (Krebs cycle) and is oxidized for energy.
The three ketone bodies, each synthesized from acetyl-CoA molecules, are: Acetoacetate, which can be converted by the liver into β-hydroxybutyrate, or spontaneously turn into acetone. Most acetoacetate is reduced to beta-hydroxybutyrate, which serves to additionally ferry reducing electrons to the tissues, especially the brain, where they are ...
The ketone bodies are released by the liver into the blood. All cells with mitochondria can take ketone bodies up from the blood and reconvert them into acetyl-CoA, which can then be used as fuel in their citric acid cycles, as no other tissue can divert its oxaloacetate into the gluconeogenic pathway in the way that the
Coenzyme A transferases (CoA-transferases) are transferase enzymes that catalyze the transfer of a coenzyme A group from an acyl-CoA donor to a carboxylic acid acceptor. [ 1 ] [ 2 ] Among other roles, they are responsible for transfer of CoA groups during fermentation and metabolism of ketone bodies .
When the liver rapidly metabolizes fatty acids into acetyl-CoA, some acetyl-CoA molecules can then be converted into ketone bodies: pyruvate, acetoacetate, beta-hydroxybutyrate, and acetone. [1] [2] These ketone bodies can function as an energy source as well as signalling molecules. [3]
The oxaloacetate is returned to mitochondrion as malate (and then converted back into oxaloacetate to transfer more acetyl-CoA out of the mitochondrion). [41] The cytosolic acetyl-CoA is carboxylated by acetyl-CoA carboxylase into malonyl-CoA, the first committed step in the synthesis of fatty acids. [41] [42]
Acetoacetyl CoA is the precursor of HMG-CoA in the mevalonate pathway, which is essential for cholesterol biosynthesis. It also takes a similar role in the ketone bodies synthesis (ketogenesis) pathway of the liver. [1] In the ketone bodies digestion pathway (in the tissue), it is no longer associated with having HMG-CoA as a product or as a ...
Acetyl-CoA is formed into malonyl-CoA by acetyl-CoA carboxylase, at which point malonyl-CoA is destined to feed into the fatty acid synthesis pathway. Acetyl-CoA carboxylase is the point of regulation in saturated straight-chain fatty acid synthesis, and is subject to both phosphorylation and allosteric regulation. Regulation by phosphorylation ...