Oxygen-18 Kinetic Isotope Effects of Nonheme Iron Enzymes HEPD and MPnS Support Iron(III) Superoxide as the Hydrogen Abstraction Species.
Nonheme iron oxygenases that carry out four-electron oxidations of substrate have been proposed to employ iron(III) superoxide species to initiate this reaction [Paria, S.; Que, L.; Paine, T. K. Angew. Chem. Int. Ed. 2011, 50, 11129]. Here we report experimental evidence in support of this proposal. (18)O KIEs were measured for two recently discovered mononuclear nonheme iron oxygenases: hydroxyethylphosphonate dioxygenase (HEPD) and methylphosphonate synthase (MPnS). Competitive (18)O KIEs measured with deuterated substrates are larger than those measured with unlabeled substrates, which indicates that C-H cleavage must occur before an irreversible reductive step at molecular oxygen. A similar observation was previously used to implicate copper(II) superoxide in the H-abstraction reactions catalyzed by dopamine β-monooxygenase [Tian, G. C.; Klinman, J. P. J. Am. Chem. Soc. 1993, 115, 8891] and peptidylglycine α-hydroxylating monooxygenase [Francisco, W. A.; Blackburn, N. J.; Klinman, J. P. Biochemistry 2003, 42, 1813].
Hui
H
Zhu
Howard Hughes Medical Institute and Department of Chemistry, University of Illinois at Urbana-Champaign , 600 South Mathews Avenue, Urbana, Illinois 61801, United States.|Institute for Genomic Biology, University of Illinois at Urbana-Champaign , 1206 West Gregory Drive, Urbana, Illinois 61801, United States.
Spencer C
SC
Peck
Florence
F
Bonnot
Howard Hughes Medical Institute and Department of Chemistry, University of Illinois at Urbana-Champaign , 600 South Mathews Avenue, Urbana, Illinois 61801, United States.|Institute for Genomic Biology, University of Illinois at Urbana-Champaign , 1206 West Gregory Drive, Urbana, Illinois 61801, United States.
Wilfred A
WA
van der Donk
Judith P
JP
Klinman
D049308:Dioxygenases / Q000378:metabolism*; D004579:Electron Transport; D006859:Hydrogen / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D010103:Oxygen Isotopes / Q000737:chemistry; D013481:Superoxides / Q000737:chemistry*
D010103:Oxygen Isotopes; D013481:Superoxides; D006859:Hydrogen; D007501:Iron; D049308:Dioxygenases