Harris W R, Carrano C J
J Inorg Biochem. 1984 Nov;22(3):201-18. doi: 10.1016/0162-0134(84)80029-x.
Human serum transferrin specifically and reversibly binds 2 equiv of vanadate at the two metal-binding sites of the protein. The vanadium(V)-transferrin complex can be formed either by the addition of vanadate to apotransferrin or by the air oxidation of the vanadyl(IV)-transferrin complex. The formation of the vanadium complex can be blocked by loading the apotransferrin with iron(III), and bound vanadium can be displaced from the protein by the subsequent addition of either gallium(III) or iron(III). The binding constant for the second equiv of vanadate is 10(6.5) in 0.1 M hepes, pH 7.4 at 25 degrees C. The binding constant for the first equiv of vanadate is probably very similar, although no quantitative value could be determined. Although transferrin reacts with the vanadate anion, studies on the transferrin model compound ethylenebis(o-hydroxyphenylglycine) indicate that at pH 9.5, the vanadium is binding at the metal-binding site as a dioxovanadium(V) cation coordinated to two phenolic residues at each binding site. This bound cation appears to be protonated over the pH range 9.5-6.5, as shown by changes in the difference uv spectrum of the transferrin complex, to produce an oxohydroxo species. Further decreases in the pH lead to dissociation of the vanadium-transferrin complex.
人血清转铁蛋白在该蛋白质的两个金属结合位点特异性且可逆地结合2当量的钒酸盐。钒（V）-转铁蛋白复合物既可以通过向脱铁转铁蛋白中添加钒酸盐形成，也可以通过钒酰（IV）-转铁蛋白复合物的空气氧化形成。钒复合物的形成可以通过用铁（III）加载脱铁转铁蛋白来阻断，并且随后添加镓（III）或铁（III）可以将结合的钒从蛋白质中置换出来。在25℃下，0.1M HEPES，pH 7.4中，第二当量钒酸盐的结合常数为10(6.5)。尽管无法确定定量值，但第一当量钒酸盐的结合常数可能非常相似。虽然转铁蛋白与钒酸根阴离子反应，但对转铁蛋白模型化合物乙二双（邻羟基苯甘氨酸）的研究表明，在pH 9.5时，钒在金属结合位点以双氧钒（V）阳离子的形式结合，在每个结合位点与两个酚残基配位。如转铁蛋白复合物的差示紫外光谱变化所示，这种结合的阳离子在pH 9.5-6.5范围内似乎被质子化，以产生氧氢氧根物种。pH进一步降低导致钒-转铁蛋白复合物解离。
