title: Characterization of a succinyl-CoA radical-cob(II)alamin spin triplet intermediate in the reaction catalyzed by adenosylcobalamin-dependent methylmalonyl-CoA mutase.
abstract: The electron paramagnetic resonance (EPR) spectrum of an intermediate freeze trapped during the steady state of the reaction catalyzed by the adenosylcobalamin (AdoCbl)-dependent enzyme, methylmalonyl-CoA mutase, has been studied. The EPR spectrum is that of a hybrid triplet spin system created as a result of strong electron-electron spin coupling between an organic radical and the low-spin Co(2+) in cob(II)alamin. The spectrum was analyzed by simulation to obtain the zero-field splitting (ZFS) parameters and Euler angles relating the radical-to-cobalt interspin vector to the g axis system of the low-spin Co(2+). Labeling of the substrate with (13)C and (2)H was used to probe the identity of the organic radical partner in the triplet spin system. The patterns of inhomogeneous broadening in the EPR signals produced by [2'-(13)C]methylmalonyl-CoA and [2-(13)C]methylmalonyl-CoA as well as line narrowing resulting from deuterium substitution in the substrate were consistent with those expected for a succinyl-CoA radical wherein the unpaired electron was centered on the carbon alpha to the free carboxyate group of the rearranged radical. The interspin distance and the Euler angles were used to position this product radical into the active site of the enzyme.
authors.affiliation: Department of Biochemistry, University of Wisconsin, Madison, Wisconsin 53726-4087, USA.
authors.forename: Steven O
authors.initials: SO
authors.lastname: Mansoorabadi
authors.forename: Rugmini
authors.initials: R
authors.lastname: Padmakumar
authors.forename: Nisso
authors.initials: N
authors.lastname: Fazliddinova
authors.forename: Monica
authors.initials: M
authors.lastname: Vlasie
authors.forename: Ruma
authors.initials: R
authors.lastname: Banerjee
authors.forename: George H
authors.initials: GH
authors.lastname: Reed
mesh_terms: D000214:Acyl Coenzyme A / Q000737:chemistry / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002247:Carbon Isotopes / Q000378:metabolism; D002384:Catalysis; D003035:Cobalt / Q000378:metabolism; D003038:Cobamides / Q000737:chemistry* / Q000378:metabolism; D003066:Coenzyme A Ligases / Q000737:chemistry / Q000378:metabolism; D003903:Deuterium / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D005609:Free Radicals / Q000737:chemistry / Q000378:metabolism; D008765:Methylmalonyl-CoA Mutase / Q000737:chemistry* / Q000378:metabolism; D008958:Models, Molecular; D013113:Spin Labels; D013379:Substrate Specificity; D014805:Vitamin B 12 / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism
chemical_list: D000214:Acyl Coenzyme A; D001426:Bacterial Proteins; D002247:Carbon Isotopes; D003038:Cobamides; D005609:Free Radicals; D013113:Spin Labels; C015357:methylmalonyl-coenzyme A; C097751:cob(II)alamin; D003035:Cobalt; D003903:Deuterium; C012046:succinyl-coenzyme A; D008765:Methylmalonyl-CoA Mutase; D003066:Coenzyme A Ligases; C021533:malonyl-CoA synthetase; C000913:cobamamide; D014805:Vitamin B 12
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