Sola M
Department of Chemistry, University of Modena, Italy.
Eur J Biochem. 1990 Dec 12;194(2):349-53. doi: 10.1111/j.1432-1033.1990.tb15625.x.
The Cd(II) derivative of ovotransferrin containing oxalate as synergistic anion was investigated through 113Cd- and 13C-NMR spectroscopy and compared with the analogous derivative obtained in the presence of bicarbonate. Cadmium loaded in the C site gives rise to a 113Cd-NMR signal at 54 ppm, while that bound to the N site is broadened beyond detection. The two resonances at 168.5 and 169.9 ppm observed in the 13C-NMR spectrum of the Cd2 derivative obtained with [13C]oxalate each correspond to slowly exchanging oxalate specifically bound to a single site. No splitting of these resonances due to 113Cd-13C magnetic coupling is observed upon insertion of 113Cd-enriched Cd(II) ion, unlike previous observations for the corresponding derivative obtained with bicarbonate as synergistic anion. It was found that the metal sites in the present derivative are inequivalent, as observed for other metal-transferrin-oxalate adducts. The C site is found to be sensitive to a residue ionization with a pKa of 9.5.
通过113Cd-和13C-NMR光谱研究了含有草酸盐作为协同阴离子的卵转铁蛋白的Cd(II)衍生物，并与在碳酸氢盐存在下获得的类似衍生物进行了比较。负载在C位点的镉在54 ppm处产生113Cd-NMR信号，而与N位点结合的镉信号变宽无法检测到。在用[13C]草酸盐获得的Cd2衍生物的13C-NMR光谱中观察到的168.5和169.9 ppm处的两个共振峰分别对应于特异性结合到单个位点的缓慢交换的草酸盐。与先前以碳酸氢盐作为协同阴离子获得的相应衍生物的观察结果不同，在插入富含113Cd的Cd(II)离子后，未观察到由于113Cd-13C磁耦合导致的这些共振峰的分裂。结果发现，与其他金属-转铁蛋白-草酸盐加合物一样，本衍生物中的金属位点是不等价的。发现C位点对pKa为9.5的残基电离敏感。
