18O kinetic isotope effects in non-heme iron enzymes: probing the nature of Fe/O2 intermediates.
Contrasted here are the competitive 18O/16O kinetic isotope effects (18O KIEs) on kcat/Km(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.
Department of Chemistry, University of California, Berkeley, California 94720, USA.
Liviu M
LM
Mirica
Kevin P
KP
McCusker
Jeffrey W
JW
Munos
Hung-wen
HW
Liu
Judith P
JP
Klinman
D002384:Catalysis; D004798:Enzymes; D007501:Iron; D007700:Kinetics; D019159:Nonheme Iron Proteins / Q000737:chemistry*; D010100:Oxygen / Q000737:chemistry*; D010103:Oxygen Isotopes / Q000737:chemistry
D004798:Enzymes; D019159:Nonheme Iron Proteins; D010103:Oxygen Isotopes; D007501:Iron; D010100:Oxygen