Use of ketones
Ketones are products of the breakdown of fatty acids under certain metabolic conditions (e.g. starvation). Ketones include acetoacetate, beta-hydroxybutyrate, and acetone. They are created only in the liver and are used by extrahepatic tissues as a temporary source of energy.
Chemical processes
Ketones are polar and are therefore freely transported in the plasma. Their utilization occurs only extrahepatically, because hepatocytes do not contain the enzyme required for their activation. First, β-hydroxybutyrate is oxidized to acetoacetate , which is subsequently activated by the transfer of coenzyme A from succinyl~CoA . Acetocetyl~CoA is converted to AcCoA (part of β-oxidation, catalyzed by thiolase), which enters the Krebs cycle.
Use of ketones by individual organs
Cardiac muscle, skeletal muscle and renal cortex prefer ketone oxidation over glucose oxidation. During starvation, the brain adapts to the burning of ketones - during long-term starvation, up to 50 % of its energy requirements are covered by the oxidation of ketones.
