Brodie A M, Ainscough E W, Baker E N, Baker H M, Shongwe M S, Smith C A
Department of Chemistry and Biochemistry, Massey University, Palmerston North, New Zealand.
Adv Exp Med Biol. 1994;357:33-44. doi: 10.1007/978-1-4615-2548-6_4.
The anion binding properties of human lactoferrin (Lf), with Fe3+ or Cu2+ as the associated metal ion, highlight differences between the two sites, and in the anion binding behaviour when different metals are bound. Carbonate, oxalate and hybrid carbonate-oxalate complexes have been prepared and their characteristic electronic and EPR spectra recorded. Oxalate can displace carbonate from either one or both anion sites of Cu2(CO3)2Lf, depending on the oxalate concentration, but no such displacement occurs for Fe2(CO3)2Lf although it does for the bovine analogue. Addition of oxalate and the appropriate metal ion to apoLf under carbonate-free conditions gives dioxalate complexes with both Fe3+ and Cu2+. The anion sites as determined from the crystal structures of Fe2(CO3)2Lf, Fe2(C2O4)2Lf, Cu2(CO3)2Lf, and Cu2(CO3)(C2O4)Lf have been compared. Both the carbonate and oxalate ions bind in bidentate fashion to the metal, except that the carbonate ion in the N-lobe site of dicupric lactoferrin is monodentate. The hybrid copper lactoferrin complex shows that the oxalate ion binds preferentially in the C-lobe site in a bidentate mode. A series of complexes containing the synergistic anion O,N-chelates with increasing substitution on the N atom (glycinate, iminodiacetate and nitrilotriacetate) have been prepared with iron bovine lactoferrin for comparison with the O,O-chelate oxalate. Overall these observations lead to a generalised model for synergistic anion binding by transferrins and allow comparisons to be made with nonsynergistic anions such as citrate and succinate.
以Fe3+或Cu2+作为相关金属离子时，人乳铁蛋白（Lf）的阴离子结合特性突出了两个位点之间的差异，以及结合不同金属时阴离子的结合行为差异。已制备了碳酸盐、草酸盐和碳酸 - 草酸盐混合配合物，并记录了它们的特征电子光谱和电子顺磁共振光谱。草酸盐可以根据其浓度从Cu2(CO3)2Lf的一个或两个阴离子位点取代碳酸盐，但对于Fe2(CO3)2Lf则不会发生这种取代，尽管牛乳铁蛋白类似物会发生这种取代。在无碳酸盐条件下，向脱铁乳铁蛋白中添加草酸盐和适当的金属离子会生成Fe3+和Cu2+的二草酸盐配合物。已比较了由Fe2(CO3)2Lf、Fe2(C2O4)2Lf、Cu2(CO3)2Lf和Cu2(CO3)(C2O4)Lf的晶体结构确定的阴离子位点。碳酸盐和草酸盐离子均以双齿方式与金属结合，只是二价铜乳铁蛋白N叶位点中的碳酸根离子是单齿的。混合铜乳铁蛋白配合物表明，草酸盐离子优先以双齿模式结合在C叶位点。已用铁牛乳铁蛋白制备了一系列含有协同阴离子O,N - 螯合物且N原子上取代度增加的配合物（甘氨酸盐、亚氨基二乙酸盐和次氮基三乙酸盐），以便与O,O - 螯合的草酸盐进行比较。总体而言，这些观察结果得出了转铁蛋白协同阴离子结合的通用模型，并允许与柠檬酸盐和琥珀酸盐等非协同阴离子进行比较。
