Felton R H, Gordon S L, Sowell A L, May S W
Biochemistry. 1984 Aug 14;23(17):3955-9. doi: 10.1021/bi00312a024.
Solvent proton nuclear magnetic dispersion studies at 25, 100, and 300 MHz have been performed on protocatechuate 3,4-dioxygenase (PCD) and its complexes with 3-chloro-4-hydroxybenzoate and 3-fluoro-4-hydroxybenzoate. Longitudinal and transverse relaxation rates were measured for these compounds and for the apoenzyme. The paramagnetic enhancement of solvent T1 is interpreted in terms of dominant dipole-dipole relaxation of fast-exchanging solvent protons with a negligible contribution from outer sphere relaxation and an electronic spin relaxation time of 0.5 ns for the high-spin ferric ion. A discrepancy between the observed T2 at 300 MHz and that calculated by assuming the usual dipolar relaxation provides evidence for an additional Curie-spin dipolar or hyperfine interaction between the proton and iron. Quantitation of the additional relaxivity provides an estimated chemical exchange lifetime of 0.1-0.14 microseconds, which suggests proton exchange by a hydroxide ligand. Proton-to-iron distances are 2.7-3.1 A in PCD and lengthen to 3.6-4.1 A in the halohydroxybenzoate complexes.
已在25兆赫、100兆赫和300兆赫下对原儿茶酸3,4 - 双加氧酶（PCD）及其与3 - 氯 - 4 - 羟基苯甲酸酯和3 - 氟 - 4 - 羟基苯甲酸酯的复合物进行了溶剂质子核磁共振色散研究。测量了这些化合物以及脱辅基酶的纵向和横向弛豫率。溶剂T1的顺磁增强被解释为快速交换溶剂质子的主导偶极 - 偶极弛豫，外球弛豫的贡献可忽略不计，高自旋铁离子的电子自旋弛豫时间为0.5纳秒。在300兆赫下观察到的T2与通过假设通常的偶极弛豫计算得到的T2之间的差异，为质子与铁之间额外的居里自旋偶极或超精细相互作用提供了证据。对额外弛豫率的定量分析得出估计的化学交换寿命为0.1 - 0.14微秒，这表明通过氢氧根配体进行质子交换。在PCD中质子到铁的距离为2.7 - 3.1埃，在卤代羟基苯甲酸酯复合物中延长至3.6 - 4.1埃。
