Biochemical effects of the hypoglycaemic compound pent-4-enoic acid and related non-hypoglycaemic fatty acids. Effects of their coenzyme A esters on enzymes of fatty acid oxidation.
1. Pent-4-enoyl-CoA and its metabolites penta-2,4-dienoyl-CoA and acryloyl-CoA, as well as n-pentanoyl-CoA, cyclopropanecarbonyl-CoA and cyclobutanecarbonyl-CoA, were examined as substrates or inhibitors of purified enzymes of beta-oxidation in an investigation to locate the site of inhibition of fatty acid oxidation by pent-4-enoate. 2. The reactions of various acyl-CoA derivatives with l-carnitine and of various acyl-l-carnitine derivatives with CoA, catalysed by carnitine acetyltransferase, were investigated and V(max.) and K(m) values were determined. Pent-4-enoyl-CoA and n-pentanoyl-CoA were good substrates, whereas cyclobutanecarbonyl-CoA, cyclopropanecarbonyl-CoA and acryloyl-CoA reacted more slowly. A very slow rate with penta-2,4-dienoyl-CoA was detected. Pent-4-enoyl-l-carnitine, n-pentanoyl-l-carnitine and cyclobutanecarbonyl-l-carnitine were good substrates and cyclopropanecarbonyl-l-carnitine reacted more slowly. 3. Pent-4-enoyl-CoA and n-pentanoyl-CoA were substrates for butyryl-CoA dehydrogenase and for octanoyl-CoA dehydrogenase, and both compounds were equally effective competitive inhibitors of these enzymes with butyryl-CoA or palmitoyl-CoA respectively as substrates. V(max.), K(m) and K(i) values were determined. 4. None of the acyl-CoA derivatives inhibited enoyl-CoA hydratase or 3-hydroxybutyryl-CoA dehydrogenase. Penta-2,4-dienoyl-CoA was a substrate for enoyl-CoA hydratase when the reaction was coupled to that catalysed by 3-hydroxybutyryl-CoA dehydrogenase. 5. In a reconstituted sequence with purified enzymes crotonoyl-CoA was largely converted into acetyl-CoA, and pent-2-enoyl-CoA into acetyl-CoA and propionyl-CoA. Penta-2,4-dienoyl-CoA was slowly converted into acetyl-CoA and acryloyl-CoA. 6. Penta-2,4-dienoyl-CoA, a unique metabolite of pent-4-enoate, was the only compound that specifically inhibited an enzyme of the beta-oxidation sequence, 3-oxoacyl-CoA thiolase. The formation of penta-2,4-dienoyl-CoA could explain the strong inhibition of fatty acid oxidation in intact mitochondria by pent-4-enoate.
D000123:Acetyltransferases / Q000378:metabolism; D000179:Acrylates; D000429:Alcohol Oxidoreductases / Q000378:metabolism; D000818:Animals; D002087:Butyrates; D002210:Caprylates; D002331:Carnitine; D002417:Cattle; D003065:Coenzyme A; D003503:Cyclobutanes; D003521:Cyclopropanes; D003864:Depression, Chemical; D004952:Esters; D005227:Fatty Acids / Q000378:metabolism / Q000494:pharmacology*; D006836:Hydro-Lyases / Q000378:metabolism; D006885:Hydroxybutyrates; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007651:Keto Acids; D007700:Kinetics; D008930:Mitochondria, Liver / Q000378:metabolism; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism; D014631:Valerates / Q000494:pharmacology*
D000179:Acrylates; D002087:Butyrates; D002210:Caprylates; D003503:Cyclobutanes; D003521:Cyclopropanes; D004952:Esters; D005227:Fatty Acids; D006885:Hydroxybutyrates; D007004:Hypoglycemic Agents; D007651:Keto Acids; D014631:Valerates; D010088:Oxidoreductases; D000429:Alcohol Oxidoreductases; D000123:Acetyltransferases; D006836:Hydro-Lyases; D002331:Carnitine; D003065:Coenzyme A