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General Background In mammals, the liver produces and excretes ketone bodies when high amounts of fatty acids derived from peripheral tissues during starvation or fasting are oxidized by beta-oxidation pathways and the amount of : ACETYL-COA produced exceeds the oxidative capacity of hepatic mitochondria, see : PWY66-367. In disease states such as diabetes mellitus, extremely high amounts of fatty acids are oxidized as a consequence of lack of insulin or insulin resistance resulting in enhanced : PWY66-367 . The ketone bodies comprise : 3-KETOBUTYRATE, : CPD-335 and : ACETONE, the last being a nonmetabolizable decarboxylation product of acetoacetate. A potentially life-threatening metabolic acidosis can occur in diabetes mellitus from excess protons provided by : 3-KETOBUTYRATE and : CPD-335, in excess of the serum bicarbonate buffering capacity . Under physiological conditions, ketone body utilization by peripheral tissues with high energy demands is essential in mammals for survival during times of starvation and extended fasting. About this Pathway This pathway describes the conversion of the ketone bodies : 3-KETOBUTYRATE and : CPD-335, to : ACETYL-COA which feeds into the : PWY66-398. Ketone bodies are more efficient energy storage molecules than glucose and ketolysis results in a lower production of reactive oxygen species and less mitochondrial stress . Ketone bodies are mostly synthesized in liver mitochondria and exported from hepatocytes for circulation to metabolizing peripheral tissues . The heart, exercising skeletal muscle and brain in starvation mode, all use ketone bodies as a major energy storage molecule. Various tissues internalize ketone bodies using a number of different monocarboxylate transporters . The major regulatory control of ketolysis occurs at three points; adipocyte lipolysis by : HS01328-MONOMER, entry of fatty acids into mitochondria by carnitine O-palmitoyltransferase 1 (which is inhibited by : MALONYL-COA) and regulation of rate-limiting : CPLX66-486 . Studies of animal models for neurodegenerative disorders including Parkinson's disease and amyotrophic lateral sclerosis (ALS) have shown that increased utilizaton of ketone bodies as fuel may reduce oxidative stress and protect against neuronal loss . Both caloric restriction and a high-fat, low carbohydrate (ketogenic) diet are being investigated as a means to reduce oxidative damage to neurons .

from BIOCYC source record: HUMAN_PWY66-368
Type: pathway
Taxonomic scope
organism-specific biosystem
Homo sapiens

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