Hirsch R E, Noble R W
Biochim Biophys Acta. 1987 Aug 21;914(3):213-9. doi: 10.1016/0167-4838(87)90280-9.
The intrinsic fluorescence of hemoglobins is known to respond to ligand-induced changes in the quaternary structure of the protein. Carp hemoglobin is an interesting model to study the quaternary transition since its R----T equilibrium is pH-dependent and at low pH, in the presence of organic phosphate, it remains in the T or 'deoxy' quaternary structure, even when saturated with ligand. In this study, using front-face fluorometry, we show that the intrinsic fluorescence intensity exhibited by carp carboxyhemoglobin increases as the pH is lowered below 6.5 in the presence of inositol hexaphosphate. At low pH, carp methemoglobin is less affected by the addition of inositol hexaphosphate than is the CO derivative, while little or no change is observed in the met-azide derivative. We conclude: (1) the exact nature of the R to T state transition induced by inositol hexaphosphate differs for carp carboxy-, met- and met-azide hemoglobin derivatives; (2) the chromophores responsible for the changes observed with absorption spectroscopy may not be the same as those chromophores responsible for the fluorescence differences; and (3) alpha 46-Trp is tentatively assigned as one source of fluorescence emission. Furthermore, fluorescence properties of carp hemoglobin are compared to those of human hemoglobin.
已知血红蛋白的固有荧光会对配体诱导的蛋白质四级结构变化做出反应。鲤鱼血红蛋白是研究四级结构转变的一个有趣模型，因为其R态到T态的平衡依赖于pH值，并且在低pH值下，在有机磷酸盐存在的情况下，即使被配体饱和，它仍保持在T态或“脱氧”四级结构。在本研究中，我们使用前表面荧光测定法表明，在肌醇六磷酸存在的情况下，当pH值降至6.5以下时，鲤鱼羧基血红蛋白表现出的固有荧光强度会增加。在低pH值下，鲤鱼高铁血红蛋白受肌醇六磷酸添加的影响比一氧化碳衍生物小，而在高铁叠氮化物衍生物中观察到很少或没有变化。我们得出以下结论：（1）肌醇六磷酸诱导的鲤鱼羧基血红蛋白、高铁血红蛋白和高铁叠氮化物血红蛋白衍生物从R态到T态转变的确切性质不同；（2）吸收光谱中观察到变化的发色团可能与导致荧光差异的发色团不同；（3）α46-色氨酸被初步确定为荧光发射的一个来源。此外，还将鲤鱼血红蛋白的荧光特性与人类血红蛋白的荧光特性进行了比较。
