Dynamics of carbon monoxide binding with neuronal nitric oxide synthase.
Dynamics of carbon monoxide binding with neuronal nitric oxide synthase.
复制标题
一氧化碳与神经元一氧化氮合酶结合的动力学。
作者：
C. Tétreau;M. Tourbez;A. Gorren;B. Mayer;D. Lavalette
本文研究了在293 ~ 77 K激光光解作用下，CO与神经元NO合成酶（nNOS）在无底物l -精氨酸和无底物l -精氨酸条件下的再结合动力学。用最大熵法确定了反应速率参数P(k)和活化焓P(H)的分布函数。在接近室温的流体溶剂中，双分子的再结合是双相的，正如先前几个小组所报道的那样。然而，旋转相关时间的测量表明，明显的双相再结合与NOS的真正动力学无关。除了天然二聚体nNOS外，另一种具有不同流体动力学特性的物种（可能是聚集或部分展开的构象）负责更快的再结合过程。在低温的刚性环境中，非本地物种的存在不影响双生的内部再结合。nNOS的CO活化焓随P(H)呈双峰分布，P(H)由两个不同的波段组成，其振幅随温度变化至77 K。这些发现与最近报道的细胞色素P-450相似，表明构象亚态的共同层次组织，每个构象亚态分裂成一个双态。因此，硫代酸协调的血红素蛋白与组氨酸协调的氧转运血红素蛋白形成鲜明对比。目前的nNOS结果为先前的论点提供了额外的支持，即硫代配体是构象亚态分裂的原因。
The dynamics of CO rebinding with neuronal NO synthase (nNOS) following laser flash photolysis have been investigated from 293 to 77 K in the absence and presence of its substrate L-arginine. The distribution functions of the rate parameters P(k) and of the activation enthalpy P(H) were determined using the maximum entropy method. In a fluid solvent near room temperature, bimolecular rebinding is biphasic, as previously reported by several groups. However, measurement of the rotational correlation time shows that the apparent biphasic rebinding is not relevant to the genuine dynamics of NOS. In addition to native dimeric nNOS, another species (possibly aggregated or partially unfolded conformation) with different hydrodynamic characteristics is responsible for the faster rebinding process. In a rigid environment at low temperature, the geminate internal rebinding is not affected by the presence of the nonnative species. nNOS exhibits a bimodal distribution of CO activation enthalpy with P(H) consisting of two distinct bands with temperature-dependent amplitudes down to 77 K. The similarity of these findings with those recently reported for cytochromes P-450 suggests a common hierarchical organization of conformational substates, with a splitting of each conformational substate into a doublet. Thus, thiolate-coordinated heme proteins are in clear contrast to histidine-coordinated oxygen-transport heme proteins. The present results with nNOS provide additional support to previous arguments incriminating the thiolate ligand as responsible for the splitting of conformational substates.