Ye Xiong, Yu Anchi, Champion Paul M
Department of Physics and Center for Interdisciplinary Research on Complex System, Northeastern University, Boston, Massachusetts 02115, USA.
J Am Chem Soc. 2006 Feb 8;128(5):1444-5. doi: 10.1021/ja057172m.
Ultrafast kinetic measurements of NO rebinding to horseradish peroxidase (HRP) are reported for the first time. The geminate kinetics are found to be exponential for all HRP samples studied. The ferric forms of HRP have NO geminate recombination time constants in the range of 15-30 ps, while the ferrous form has a time constant of approximately 7 ps. The simple exponential NO geminate kinetics found for HRP demonstrate that heme relaxation is not the underlying source of the nonexponential NO rebinding in myoglobin (Mb). The NO ligand escape rates from HRP are also determined, and they are found to depend dramatically on the presence or absence of the competitive inhibitor benzohydroxamic acid (BHA). The kinetic results indicate that, in contrast to Mb, there is direct solvent access to the distal heme pocket of HRP.
首次报道了对一氧化氮(NO)与辣根过氧化物酶(HRP)重新结合的超快动力学测量。对于所有研究的HRP样品,发现双分子动力学呈指数形式。HRP的铁离子形式的NO双分子复合时间常数在15 - 30皮秒范围内,而亚铁形式的时间常数约为7皮秒。在HRP中发现的简单指数型NO双分子动力学表明,血红素弛豫不是肌红蛋白(Mb)中NO重新结合非指数形式的潜在原因。还测定了NO从HRP的配体逃逸速率,发现它们极大地依赖于竞争性抑制剂苯并异羟肟酸(BHA)的存在与否。动力学结果表明,与Mb不同,溶剂可直接进入HRP的远端血红素口袋。