Cannon J C, Chasteen N D
Biochemistry. 1975 Oct 21;14(21):4573-7. doi: 10.1021/bi00692a003.
Vanadyl ion, VO(IV), has been used as an electron paramagnetic resonance (EPR) spin label to study the metal-binding properties of human serum transferrin in the presence of bicarbonate. Iron-saturated transferrin does not bind the vanadyl ion. Room temperature titrations of apotransferrin with VO(IV) as monitored by EPR indicate the extent of binding to be pH dependent, with a full 0.2 VO(IV) ions per transferrin molecule bound at pH 7.5 and 9, but only about 1.2 VO(IV) ions bound at pH 6. The EPR spectra of frozen solutions with or without 0.1 M NaCUO4 at 77 K show that there are two spectroscopically nonequivalent binding sites (A and B) with a slight difference in binding constants. One site (A site) exhibits essentially constant binding capacity in the pH range 6-9, but the other (B site) becomes less avialable as the pH is reduced below 7. Results with mixed Fe(III)-VO(IV) transferrin complexes suggest that iron shows a slight tendency to bind at the B site over the A site pH 7.5 and 9.0. Only the B site in both vanadyl and iron transferrins is perturbed by the presence of perchlorate.
钒离子VO(IV)已被用作电子顺磁共振（EPR）自旋标记物，以研究在碳酸氢盐存在下人类血清转铁蛋白的金属结合特性。铁饱和的转铁蛋白不结合钒离子。通过EPR监测，在室温下用VO(IV)对脱铁转铁蛋白进行滴定，结果表明结合程度取决于pH值，在pH 7.5和9时，每个转铁蛋白分子可结合0.2个VO(IV)离子，但在pH 6时仅约结合0.12个VO(IV)离子。在77 K下，含有或不含有0.1 M NaCUO4的冷冻溶液的EPR光谱表明，存在两个光谱学上不等价的结合位点（A和B），其结合常数略有差异。一个位点（A位点）在pH 6-9范围内表现出基本恒定的结合能力，但另一个位点（B位点）在pH降至7以下时变得不太容易结合。Fe(III)-VO(IV)混合转铁蛋白复合物的结果表明，在pH 7.5和9.0时，铁在B位点上的结合倾向略高于A位点。只有钒酰转铁蛋白和铁转铁蛋白中的B位点会受到高氯酸盐的影响。
