Open AccessOxygen-18 Kinetic Isotope Effects of Nonheme Iron Enzymes HEPD and MPnS Support Iron(III) Superoxide as the Hydrogen Abstraction Species
Author(s) -
HaiLiang Zhu,
Spencer C. Peck,
F. Bonnot,
Wilfred A. van der Donk,
Judith P. Klinman
Publication year - 2015
Publication title -
journal of the american chemical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 7.115
H-Index - 612
eISSN - 1520-5126
pISSN - 0002-7863
DOI - 10.1021/jacs.5b03907
Subject(s) - chemistry , dioxygenase , superoxide , oxygenase , kinetic isotope effect , hydrogen atom abstraction , stereochemistry , monooxygenase , oxygen , methane monooxygenase , substrate (aquarium) , enzyme , deuterium , hydrogen , biochemistry , organic chemistry , cytochrome p450 , physics , oceanography , quantum mechanics , geology
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].