Wagner G, DeMarco A, Wüthrich K
Biophys Struct Mech. 1976 Aug 23;2(2):139-58. doi: 10.1007/BF00863706.
The basic pancreatic trypsin inhibitor (BPTI) was investigated by high resolution 1H NMR techniques at 360 MHz. Observation of the amide proton resonances of the polypeptide backbone showed that the globular conformation of BPTI determined by X-ray studies in single crystals is maintained in aqueous solution over the temperature range from 4 degrees to 87 degrees. NMR studies over this temperature range of the aromatic amino acid residues of BPTI. i.e. 4 tyrosines and 4 phenylalanines, led to complete assignments of all the aromatic spin systems in the protein. From this, information was obtained on the rotational motions about the C beta--Cv bond axis of the aromatic rings in the globular form of PBTI. At 25 degrees, two tyrosine rings and one phenylalanine ring are rotating rapidly on the NMR time scale. For the other rings the transitions from slow to rapid rotational motions were investigated at variable temperatures and energy barriers for these intramolecular rate processes determined. The studies of the tyrosine resonances had been described in detail in a previous publication. The present paper describes the identification of the phenylalanine resonances and comments on some technical aspects which might be of quite general interest for the analysis of highly resolved 1H NMR spectra of proteins. Data for the tyrosines and the phenylalanines are compiled in three tables, i.e. the pK alpha-values for the tyrosines, the NMR parameters for all eight aromatics, and the parameters delta G not equal to, and, where available, delta H not equal to and delta S not equal to for the rotational motions of the rings.
采用360兆赫的高分辨率1H核磁共振技术对基本胰蛋白酶抑制剂（BPTI）进行了研究。对多肽主链酰胺质子共振的观察表明，通过单晶X射线研究确定的BPTI的球状构象在4摄氏度至87摄氏度的温度范围内在水溶液中得以保持。对BPTI的芳香族氨基酸残基在该温度范围内进行核磁共振研究。即4个酪氨酸和4个苯丙氨酸，从而完成了该蛋白质中所有芳香族自旋系统的归属。由此获得了关于PBTI球状形式中芳香环围绕Cβ - Cγ键轴的旋转运动的信息。在25摄氏度时，两个酪氨酸环和一个苯丙氨酸环在核磁共振时间尺度上快速旋转。对于其他环，在可变温度下研究了从慢速到快速旋转运动的转变，并确定了这些分子内速率过程的能垒。酪氨酸共振的研究已在先前的一篇出版物中详细描述。本文描述了苯丙氨酸共振的鉴定，并对一些技术方面进行了评论，这些方面可能对蛋白质高分辨率1H核磁共振谱的分析具有普遍意义。酪氨酸和苯丙氨酸的数据汇总在三个表格中，即酪氨酸的pKα值、所有八个芳香族的核磁共振参数，以及环旋转运动的参数ΔG≠、以及（如有）ΔH≠和ΔS≠。
