title: Interaction of the fluorescent analogue stearoyl-(1,N6)-etheno coenzyme A with chicken liver acetyl coenzyme A carboxylase.
abstract: The interaction of stearoyl-(1,N6)-etheno coenzyme A (stearoyl-epsilon-CoA) with acetyl coenzyme A carboxylase was investigated by using fluorescence spectroscopy. The fluorescence emission of stearoyl-epsilon-CoA was partially quenched by acetyl coenzyme A carboxylase. Analysis of the data for dissociation constant (KD) and the stoichiometry of the interaction (n) gave values of 5.06 nM and 1.2, respectively, at pH 7.6 in 50 mM Tris-HCl and 25 degrees C. The KD value is comparable to the inhibition constant (Ki) obtained previously by others for the inhibition of rat liver acetyl coenzyme A carboxylase by long chain fatty acyl-CoAs. Citrate (which is known to polymerize and thus activate carboxylase) caused a partial quenching of the protein fluorescence of carboxylase, presumably due to polymerization of the enzyme. The quenching of the stearoyl-epsilon-CoA fluorescence caused by carboxylase as well as the inhibition of carboxylase activity by stearoyl-epsilon-CoA was reversed by citrate, but only in the presence of 6-O-methylglucose polysaccharide which forms a stable complex with fatty acyl-CoA. This shows that the stearoyl-epsilon-CoA bound to the enzyme is displaced by citrate only in the presence of an acceptor of fatty acyl-CoA. These results support the reciprocal relationship of citrate and fatty acyl-CoA in the regulation of acetyl coenzyme A carboxylase.
mesh_terms: D000103:Acetyl-CoA Carboxylase / Q000378:metabolism*; D000214:Acyl Coenzyme A; D000818:Animals; D002645:Chickens; D007700:Kinetics; D008025:Ligases / Q000378:metabolism*; D008099:Liver / Q000201:enzymology*; D011485:Protein Binding; D013050:Spectrometry, Fluorescence
chemical_list: D000214:Acyl Coenzyme A; C024285:stearoyl-(1,N(6))-etheno-coenzyme A; D008025:Ligases; D000103:Acetyl-CoA Carboxylase