4-bromotiglic acid, a novel inhibitor of thiolases and a tool for assessing the cooperation between the membrane-bound and soluble beta-oxidation systems of rat liver mitochondria.
An inhibitor of long-chain 3-ketoacyl-CoA thiolase has been developed as a tool for probing the cooperation between the two fatty acid beta-oxidation systems located in the inner mitochondrial membrane and in the mitochondrial matrix, respectively. 4-Bromotiglic acid was synthesized and found to inhibit palmitoylcarnitine-supported respiration of rat liver mitochondria in concentration-dependent and time-dependent fashions. Complete inhibition of respiration was achieved after incubating coupled mitochondria with 10 microM 4-bromotiglic acid for 2 min. Uncoupled mitochondria were resistant to the toxic effect of the inhibitor. Inhibition of octanoate-supported or octanoylcarnitine-supported respiration was partially reversed when the inhibitor was removed from the incubation medium. Such reversal was not observed with either palmitoylcarnitine or 2-methyldecanoic acid as the respiratory substrate. The severity of the irreversible inhibition declined with decreasing chain length of the acylcarnitine substrate. Of all beta-oxidation enzymes, only thiolases were inactivated by the inhibitor. Under conditions at which acetoacetyl-CoA thiolase and long-chain thiolase were completely inactivated, 3-ketoacyl-CoA thiolase retained some activity. It is concluded that the degradation of palmitic acid and longer-chain fatty acids is initiated by the beta-oxidation system of the inner membrane, whereas fatty acids shorter than palmitic acid can be oxidized to a certain degree by the matrix system alone. The effectiveness of the matrix system increases with decreasing chain length of the substrate.
Liang
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Department of Chemistry, City College of the City University of New York 10031, USA.
Schulz
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H
D015094:3-Hydroxyacyl CoA Dehydrogenases / Q000037:antagonists & inhibitors; D000102:Acetyl-CoA C-Acyltransferase / Q000037:antagonists & inhibitors*; D000818:Animals; D003437:Crotonates / Q000138:chemical synthesis / Q000494:pharmacology*; D004746:Enoyl-CoA Hydratase / Q000037:antagonists & inhibitors; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000138:chemical synthesis / Q000494:pharmacology*; D005227:Fatty Acids / Q000378:metabolism*; D007425:Intracellular Membranes / Q000187:drug effects / Q000201:enzymology*; D008930:Mitochondria, Liver / Q000187:drug effects / Q000201:enzymology*; D063991:Mitochondrial Trifunctional Protein; D009097:Multienzyme Complexes / Q000378:metabolism*; D010084:Oxidation-Reduction / Q000187:drug effects; D051381:Rats; D012995:Solubility
C115522:4-bromotiglic acid; D003437:Crotonates; D004791:Enzyme Inhibitors; D005227:Fatty Acids; D009097:Multienzyme Complexes; D015094:3-Hydroxyacyl CoA Dehydrogenases; D000102:Acetyl-CoA C-Acyltransferase; D063991:Mitochondrial Trifunctional Protein; D004746:Enoyl-CoA Hydratase