title: A novel reaction between adenosylcobalamin and 2-methyleneglutarate catalyzed by glutamate mutase.
abstract: We describe a novel reaction of adenosylcobalamin that occurs when adenosylcobalamin-dependent glutamate mutase is reacted with the substrate analogue 2-methyleneglutarate. Although 2-methyleneglutarate is a substrate for the closely related adenosylcobalamin-dependent enzyme 2-methyleneglutarate mutase, it reacts with glutamate mutase to cause time-dependent inhibition of the enzyme. Binding of 2-methyleneglutarate to glutamate mutase initiates homolysis of adenosylcobalamin. However, instead of the adenosyl radical proceeding to abstract a hydrogen from the substrate, which is the next step in all adenosylcobalamin-dependent enzymes, the adenosyl radical undergoes addition to the exo-methylene group to generate a tertiary radical at C-2 of methyleneglutarate. This radical has been characterized by EPR spectroscopy with regiospecifically (13)C-labeled methyleneglutarates. Irreversible inhibition of the enzyme appears to be a complicated process, and the detailed chemical and kinetic mechanism remains to be elucidated. The kinetics of this process suggest that cob(II)alamin may reduce the enzyme-bound organic radical so that stable adducts between the adenosyl moiety of the coenzyme and 2-methyleneglutarate are formed.
authors.affiliation: Department of Chemistry and Division of Biophysics, University of Michigan, Ann Arbor, Michigan 48109-1055, USA.
authors.forename: Marja S
authors.initials: MS
authors.lastname: Huhta
authors.forename: Daniele
authors.initials: D
authors.lastname: Ciceri
authors.forename: Bernard T
authors.initials: BT
authors.lastname: Golding
authors.forename: E Neil G
authors.initials: EN
authors.lastname: Marsh
mesh_terms: D002384:Catalysis; D003038:Cobamides / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005977:Glutarates / Q000378:metabolism* / Q000494:pharmacology; D019751:Intramolecular Transferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet; D013379:Substrate Specificity; D013386:Succinates / Q000378:metabolism; D014316:Tritium / Q000378:metabolism
chemical_list: D003038:Cobamides; D004791:Enzyme Inhibitors; D005977:Glutarates; D013386:Succinates; D014316:Tritium; C048646:3-methylitaconate; C002172:2-methyleneglutaric acid; D019751:Intramolecular Transferases; C021570:methylaspartate mutase; C000913:cobamamide