Labro J F, Janssen L H
Biochim Biophys Acta. 1986 Sep 26;873(2):267-78. doi: 10.1016/0167-4838(86)90054-3.
By means of 500 MHz 1H-NMR spectroscopy detailed information has been obtained about the proton titration behaviour of the histidine residues of human serum albumin under various experimental conditions. The approximate number of His C2 protons resolved varied from 11 at pH* 9.0 to 16 at pH* 5.5. The latter is the same as the number of histidine residues reported to be present in the molecule. The symbol pH* stands for the meter readings uncorrected for the deuterium isotope effect. Whereas some of the NMR signals remained visible over the entire pH* range examined (5-9), others, having pH*-dependent resonance intensities, were observed in part of the pH* range only. The latter effect is indicative of an alteration in the histidine environment in the course of pH* titration. It is thought that the so-called N-B conformational transition, occurring in the neutral pH region, is responsible for this alteration. The spectral effects observed upon the addition of Ca2+ can be interpreted in terms of a downward pK* shift for a number of histidine residues and a concomitant downward shift in the midpoint pH* of the N-B transition. This corroborates the results of previous investigations on this matter.
通过500兆赫的1H-核磁共振光谱法，已获得了在各种实验条件下人血清白蛋白组氨酸残基的质子滴定行为的详细信息。分辨出的His C2质子的近似数量从pH* 9.0时的11个到pH* 5.5时的16个不等。后者与据报道分子中存在的组氨酸残基数量相同。符号pH代表未校正氘同位素效应的仪表读数。虽然一些核磁共振信号在所研究的整个pH范围（5 - 9）内都可见，但其他具有pH依赖性共振强度的信号仅在部分pH范围内被观察到。后一种效应表明在pH滴定过程中组氨酸环境发生了改变。据认为，在中性pH区域发生的所谓N - B构象转变是造成这种改变的原因。加入Ca2+后观察到的光谱效应可以解释为一些组氨酸残基的pK向下移动以及N - B转变的中点pH*随之向下移动。这证实了先前关于此事的研究结果。
