18O Kinetic Isotope Effects in Non-Heme Iron Enzymes: Probing the Nature of Fe/O2 Intermediates

• Published in: Journal of the American Chemical Society Vol. 130; no. 26; pp. 8122 - 8123
• Main Authors: Mirica, Liviu M, McCusker, Kevin P, Munos, Jeffrey W, Liu, Hung-wen, Klinman, Judith P
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 02.07.2008
• Subjects: Catalysis; Enzymes; Iron; Kinetics; Nonheme Iron Proteins - chemistry; Oxygen - chemistry; Oxygen Isotopes - chemistry
• ISSN: 0002-7863; 1520-5126
• DOI: 10.1021/ja800265s

Contrasted here are the competitive 18O/16O kinetic isotope effects (18O KIEs) on k cat/K m(O2) for three non-heme iron enzymes that activate O2 at an iron center coordinated by a 2-His-1-carboxylate facial triad: taurine dioxygenase (TauD), (S)-(2)-hydroxypropylphosphonic acid epoxidase (HppE), and 1-aminocyclopropyl-1-carboxylic acid oxidase (ACCO). Measured 18O KIEs of 1.0102 ± 0.0002 (TauD), 1.0120 ± 0.0002 (HppE), and 1.0215 ± 0.0005 (ACCO) suggest the formation in the rate-limiting step of O2 activation of an FeIII-peroxohemiketal, FeIII−OOH, and FeIVO species, respectively. The comparison of the measured 18O KIEs with calculated or experimental 18O equilibrium isotope effects (18O EIEs) provides new insights into the O2 activation through an inner-sphere mechanism at a non-heme iron center.