title: Inhibition in vitro of acyl-CoA dehydrogenases by 2-mercaptoacetate in rat liver mitochondria.
abstract: In rat liver hypo-osmotically treated mitochondria, 2-mercaptoacetate inhibits respiration induced by palmitoyl-CoA, octanoate or butyryl-CoA only when the reaction medium is supplemented with ATP. Under this condition, NADH-stimulated respiration is not affected. In liver mitochondrial matrix, the presence of ATP is also required to observe a 2-mercaptoacetate-induced inhibition of acyl-CoA dehydrogenases tested with palmitoyl-CoA, butyryl-CoA or isovaleryl-CoA as substrate. As the oxidation of these substrates is also inhibited by the incubation medium resulting from the reaction of 2-mercaptoacetate with acetyl-CoA synthase, with conditions under which 2-mercaptoacetate has no effect, 2-mercaptoacetyl-CoA seems to be the likely inhibitory metabolite responsible for the effects of 2-mercaptoacetate. Kinetic experiments show that the main effect of the 2-mercaptoacetate-active metabolite is to decrease the affinities of fatty acyl-CoA dehydrogenases towards palmitoyl-CoA or butyryl-CoA and of isovaleryl-CoA dehydrogenase towards isovaleryl-CoA. Addition of N-ethylmaleimide to mitochondrial matrix pre-exposed to 2-mercaptoacetate results in the immediate reversion of the inhibitions of palmitoyl-CoA and isovaleryl-CoA dehydrogenations and in a delayed reversion of butyryl-CoA dehydrogenation. These results led us to conclude that (i) the ATP-dependent conversion of 2-mercaptoacetate into an inhibitory metabolite takes place in the liver mitochondrial matrix and (ii) the three fatty acyl-CoA dehydrogenases and isovaleryl-CoA dehydrogenase are mainly competitively inhibited by this compound. Finally, the present study also suggests that the inhibitory metabolite of 2-mercaptoacetate may bind non-specifically to, or induce conformational changes at, the acyl-CoA binding sites of these dehydrogenases.
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism; D000818:Animals; D005033:Ethylmaleimide / Q000494:pharmacology; D044943:Fatty Acid Desaturases / Q000037:antagonists & inhibitors*; D005227:Fatty Acids / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D007700:Kinetics; D008930:Mitochondria, Liver / Q000187:drug effects / Q000201:enzymology*; D009243:NAD / Q000378:metabolism; D010171:Palmitoyl Coenzyme A / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013864:Thioglycolates / Q000494:pharmacology*
chemical_list: D000214:Acyl Coenzyme A; D005227:Fatty Acids; D013864:Thioglycolates; D009243:NAD; D010171:Palmitoyl Coenzyme A; C024343:butyryl-coenzyme A; C017447:isovaleryl-coenzyme A; C017487:2-mercaptoacetate; D044943:Fatty Acid Desaturases; D005033:Ethylmaleimide