Morozova Olga B, Hore P J, Sagdeev Renad Z, Yurkovskaya Alexandra V
International Tomography Center of SB RAS, 630090, Institutskaya 3a, Novosibirsk, Russia.
J Phys Chem B. 2005 Nov 24;109(46):21971-8. doi: 10.1021/jp053394v.
The kinetics of the chemically induced dynamic nuclear polarization (CIDNP) produced in reactions of hen lysozyme with photosensitizers have been studied for the native state of the protein at pH 3.8 and for two denatured states. The latter were generated by raising the temperature to 80 degrees C or by combining a temperature rise (to 50 degrees C) with the addition of chemical denaturant (10 M urea). Detailed analysis of the CIDNP time dependence on a microsecond time scale revealed that, in both denatured states, intramolecular electron transfer (IET) from a tyrosine residue to the cation radical of a tryptophan residue (rate constant k(f)) is highly efficient and plays a decisive role in the evolution of the nuclear polarization. To describe the observed CIDNP kinetics with a self-consistent set of parameters, IET in the reverse direction, from a tryptophan residue to a tyrosine residue radical (rate constant k(r)), has also to be taken into account. The IET rate constants determined by analysis of the CIDNP kinetics are, at 80 degrees C: k(f) = 1 x 10(5) s(-1) and k(r) = 1 x 10(4) s(-1); at 50 degrees C in the presence of 10 M urea: k(f) = 7 x 10(4) s(-1), k(r) = 1 x 10(4) s(-1). IET does not appear to influence the CIDNP kinetics of the native state.
在pH值为3.8的条件下，对天然状态的鸡蛋清溶菌酶与光敏剂反应中产生的化学诱导动态核极化（CIDNP）动力学进行了研究，并对两种变性状态进行了研究。后两种状态是通过将温度升至80℃或通过将温度升至50℃并添加化学变性剂（10 M尿素）产生的。对微秒时间尺度上CIDNP时间依赖性的详细分析表明，在两种变性状态下，从酪氨酸残基到色氨酸残基阳离子自由基的分子内电子转移（IET）（速率常数k(f)）非常高效，并且在核极化的演变中起决定性作用。为了用一组自洽的参数描述观察到的CIDNP动力学，还必须考虑反向的IET，即从色氨酸残基到酪氨酸残基自由基（速率常数k(r)）。通过对CIDNP动力学分析确定的IET速率常数，在80℃时：k(f) = 1×10⁵ s⁻¹，k(r) = 1×10⁴ s⁻¹；在50℃且存在10 M尿素时：k(f) = 7×10⁴ s⁻¹，k(r) = 1×10⁴ s⁻¹。IET似乎不影响天然状态的CIDNP动力学。
