Biochemical effects of the hypoglycaemic compound pent-4-enoic acid and related non-hypoglycaemic fatty acids. Effects of the free acids and their carnitine esters on coenzyme A-dependent oxidations in rat liver mitochondria.
1. The synthesis of pent-4-enoyl-l-carnitine, cyclopropanecarbonyl-l-carnitine and cyclobutanecarbonyl-l-carnitine is described. 2. Pent-4-enoate strongly inhibits palmitoyl-l-carnitine oxidation in coupled but not in uncoupled mitochondria. Pent-4-enoyl-l-carnitine strongly inhibits palmitoyl-l-carnitine oxidation in uncoupled mitochondria. Prior intramitochondrial formation of pent-4-enoyl-CoA is therefore necessary for inhibition. 3. There was a small self-limiting pulse of oxidation of pent-4-enoyl-l-carnitine during which the ability to inhibit the oxidation of subsequently added palmitoyl-l-carnitine developed. 4. Pent-4-enoate and pent-4-enoyl-l-carnitine are equally effective inhibitors of the oxidation of all even-chain acylcarnitines of chain length C(4)-C(16). Pent-4-enoyl-l-carnitine also inhibits the oxidation of pyruvate and of 2-oxoglutarate. 5. Pent-4-enoate strongly inhibits the oxidation of palmitate but not that of octanoate. This is presumably due to competition between octanoate and pent-4-enoate for medium-chain acyl-CoA ligase. 6. There was less inhibition of the oxidation of pyruvate by pent-4-enoyl-l-carnitine, and of palmitoyl-l-carnitine by cyclopropanecarbonyl-l-carnitine, after pre-incubation with 10mm-arsenate. This suggests that these inhibitions were caused either by depletion of free CoA or by increase of acyl-CoA concentrations, since arsenate deacylates intramitochondrial acyl-CoA. There was little effect on the inhibition of palmitoyl-l-carnitine oxidation by pent-4-enoyl-l-carnitine. 7. Penta-2,4-dienoate strongly inhibited palmitoyl-l-carnitine oxidation in coupled mitochondria; acrylate only inhibited slightly. 8. Pent-4-enoate (0.1mm) caused a rapid and almost complete decrease in free CoA and a large increase in acid-soluble acyl-CoA when incubated with coupled mitochondria. Cyclopropanecarboxylate caused a similar decrease in CoA, with an equivalent rise in acid-soluble acyl-CoA concentrations. n-Pentanoate caused extensive lowering of CoA and a large increase in acid-soluble acyl-CoA and acetyl-CoA concentrations. Octanoate caused a 50% lowering of CoA and an increase in acid-soluble acyl-CoA and acetyl-CoA concentrations. 9. Cyclopropanecarboxylate and n-pentanoate were less potent inhibitors of palmitate oxidation than was pent-4-enoate. 10. It is concluded that pent-4-enoate causes a specific inhibition of beta-oxidation after the formation intramitochondrially of its metabolites.
D000818:Animals; D002331:Carnitine / Q000096:biosynthesis / Q000494:pharmacology*; D003065:Coenzyme A / Q000096:biosynthesis; D003503:Cyclobutanes / Q000378:metabolism; D003521:Cyclopropanes / Q000378:metabolism; D003864:Depression, Chemical; D004952:Esters / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D066298:In Vitro Techniques; D007656:Ketoglutaric Acids / Q000378:metabolism; D008297:Male; D008930:Mitochondria, Liver / Q000378:metabolism*; D010084:Oxidation-Reduction; D010169:Palmitic Acids / Q000378:metabolism; D011773:Pyruvates / Q000378:metabolism; D051381:Rats; D014631:Valerates / Q000494:pharmacology*
D003503:Cyclobutanes; D003521:Cyclopropanes; D004952:Esters; D005231:Fatty Acids, Unsaturated; D007004:Hypoglycemic Agents; D007656:Ketoglutaric Acids; D010169:Palmitic Acids; D011773:Pyruvates; D014631:Valerates; D002331:Carnitine; D003065:Coenzyme A