Mirica Liviu M, McCusker Kevin P, Munos Jeffrey W, Liu Hung-wen, Klinman Judith P
Department of Chemistry, University of California, Berkeley, California 94720, USA.
J Am Chem Soc. 2008 Jul 2;130(26):8122-3. doi: 10.1021/ja800265s. Epub 2008 Jun 7.
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.
本文对比了三种非血红素铁酶在kcat/Km(O2)上的竞争性18O/16O动力学同位素效应（18O KIEs），这三种酶在由2-组氨酸-1-羧酸盐面三联体配位的铁中心激活O2：牛磺酸双加氧酶（TauD）、（S）-（2）-羟丙基膦酸环氧化酶（HppE）和1-氨基环丙烷-1-羧酸氧化酶（ACCO）。测得的18O KIEs分别为1.0102±0.0002（TauD）、1.0120±0.0002（HppE）和1.0215±0.0005（ACCO），这表明在O2激活的限速步骤中分别形成了FeIII-过氧半缩酮、FeIII-OOH和FeIV O物种。将测得的18O KIEs与计算的或实验的18O平衡同位素效应（18O EIEs）进行比较，为通过非血红素铁中心的内球机制激活O2提供了新的见解。
