title: Binding, hydration, and decarboxylation of the reaction intermediate glutaconyl-coenzyme A by human glutaryl-CoA dehydrogenase.
abstract: Glutaconyl-coenzyme A (CoA) is the presumed enzyme-bound intermediate in the oxidative decarboxylation of glutaryl-CoA that is catalyzed by glutaryl-CoA dehydrogenase. We demonstrated glutaconyl-CoA bound to glutaryl-CoA dehydrogenase after anaerobic reduction of the dehydrogenase with glutaryl-CoA. Glutaryl-CoA dehydrogenase also has intrinsic enoyl-CoA hydratase activity, a property of other members of the acyl-CoA dehydrogenase family. The enzyme rapidly hydrates glutaconyl-CoA at pH 7.6 with a k(cat) of 2.7 s(-1). The k(cat) in the overall oxidation-decarboxylation reaction at pH 7.6 is about 9 s(-1). The binding of glutaconyl-CoA was quantitatively assessed from the K(m) in the hydratase reaction, 3 microM, and the K(i), 1.0 microM, as a competitive inhibitor of the dehydrogenase. These values compare with K(m) and K(i) of 4.0 and 12.9 microM, respectively, for crotonyl-CoA. Glu370 is the general base catalyst in the dehydrogenase that abstracts an alpha-proton of the substrate to initiate the catalytic pathway. The mutant dehydrogenase, Glu370Gln, is inactive in the dehydrogenation and the hydratase reactions. However, this mutant dehydrogenase decarboxylates glutaconyl-CoA to crotonyl-CoA without oxidation-reduction reactions of the dehydrogenase flavin. Addition of glutaconyl-CoA to this mutant dehydrogenase results in a rapid, transient increase in long-wavelength absorbance (lambda(max) approximately 725 nm), and crotonyl-CoA is found as the sole product. We propose that this 725 nm-absorbing species is the delocalized crotonyl-CoA anion that follows decarboxylation and that the decay is the result of slow protonation of the anion in the absence of the general acid catalyst, Glu370(H(+)). In the absence of detectable oxidation-reduction, the data indicate that oxidation-reduction of the dehydrogenase flavin is not essential for decarboxylation of glutaconyl-CoA.
authors.affiliation: The Program in Human Medical Genetics, The Department of Pediatrics, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
authors.forename: J B
authors.initials: JB
authors.lastname: Westover
authors.forename: S I
authors.initials: SI
authors.lastname: Goodman
authors.forename: F E
authors.initials: FE
authors.lastname: Frerman
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism*; D003653:Decarboxylation; D050770:Glutaryl-CoA Dehydrogenase; D006801:Humans; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D044925:Oxidoreductases Acting on CH-CH Group Donors; D011485:Protein Binding; D011994:Recombinant Proteins / Q000378:metabolism
chemical_list: D000214:Acyl Coenzyme A; D011994:Recombinant Proteins; C032423:glutaconyl-coenzyme A; D010088:Oxidoreductases; D044925:Oxidoreductases Acting on CH-CH Group Donors; D050770:Glutaryl-CoA Dehydrogenase