title: Metabolism of 4-pentenoic acid and inhibition of thiolase by metabolites of 4-pentenoic acid.
abstract: The metabolism of 4-pentenoic acid, a hypoglycemic agent and inhibitor of fatty acid oxidation, has been studied in rat heart mitochondria. Confirmed was the conversion of 4-pentenoic acid to 2,4-pentadienoyl coenzyme A (CoA), which either is directly degraded via beta-oxidation or is first reduced in a NADPH-dependent reaction before it is further degraded by beta-oxidation. At pH 6.9, the NADPH-dependent reduction of 2,4-pentadienoyl-CoA proceeds 10 times faster than its degradation by beta-oxidation. At pH 7.8, this ratio is only 2 to 1. The direct beta-oxidation of 2,4-pentadienoyl-CoA leads to the formation of 3-keto-4-pentenoyl-CoA, which is highly reactive and spontaneously converts to another 3-ketoacyl-CoA derivative (compound X). 3-Keto-4-pentenoyl-CoA is a poor substrate of 3-ketoacyl-CoA thiolase (EC 2.3..1.16) whereas compound X is not measurably acted upon by this enzyme. The effects of several metabolites of 4-pentenoic acid on the activity of 3-ketoacyl-CoA thiolase were studied. 3,4-Pentadienoyl-CoA is a weak inhibitor of this enzyme that is protected against the inhibition by acetoacetyl-CoA. The most effective inhibitor of 3-ketoacyl-CoA thiolase was found to be 3-keto-4-pentenoyl-CoA, which inhibits the enzyme in both a reversible and irreversible manner. The reversible inhibition is possibly a consequence of the inhibitor being a poor substrate of 3-ketoacyl-CoA thiolase. It is concluded that 4-pentenoic acid is metabolized in mitochondria by two pathways. The minor yields 3-keto-4-pentenoyl-CoA, which acts both as a reversible and as a irreversible inhibitor of 3-ketoacyl-CoA thiolase and consequently of fatty acid oxidation.
mesh_terms: D000101:Acetyl-CoA C-Acetyltransferase / Q000037:antagonists & inhibitors*; D000102:Acetyl-CoA C-Acyltransferase / Q000037:antagonists & inhibitors*; D000123:Acetyltransferases / Q000037:antagonists & inhibitors*; D000217:Acyltransferases / Q000037:antagonists & inhibitors*; D000818:Animals; D005229:Fatty Acids, Monounsaturated; D005231:Fatty Acids, Unsaturated / Q000378:metabolism* / Q000494:pharmacology; D007700:Kinetics; D008929:Mitochondria, Heart / Q000201:enzymology*; D051381:Rats; D013329:Structure-Activity Relationship; D013552:Swine
chemical_list: D005229:Fatty Acids, Monounsaturated; D005231:Fatty Acids, Unsaturated; C009785:4-pentenoic acid; D000217:Acyltransferases; D000123:Acetyltransferases; D000102:Acetyl-CoA C-Acyltransferase; D000101:Acetyl-CoA C-Acetyltransferase