Zhong Weiqing, Parkinson John A, Guo Maolin, Sadler Peter J
Department of Chemistry, The University of Edinburgh, King's Buildings, West Mains Road, UK.
J Biol Inorg Chem. 2002 Jun;7(6):589-99. doi: 10.1007/s00775-001-0337-8. Epub 2002 Feb 15.
Human serum apotransferrin (hTF) binds to Zr(IV) slowly in the presence of nitrilotriacetate (NTA), citrate or ethylenediaminetetraacetate (EDTA) as donor ligands. For Zr(NTA)(2)(2-) as donor, equilibrium was reached in ca. 2 h (pH 7.4, 298 K, 10 mM Hepes, 5 mM bicarbonate) and full loading of the N- and C-lobe sites was achievable to give Zr(2)-hTF. (13)C NMR data suggest that carbonate can bind as a synergistic anion. (1)H and 2D [(1)H,(13)C] (using epsilon-[(13)C]Met-hTF) NMR studies show that there is little lobe-selectively in the order of Zr(IV) uptake. Fe(III) displaced Zr(IV) from the C-lobe of Zr(2)-hTF first, followed by the N-lobe. However, in the presence of a large excess of NTA, Zr(IV) binds to the N-lobe of holo-hTF (Fe(2)-hTF) first followed by the C-lobe. The (1)H and (13)C NMR chemical shift changes for epsilon-[(13)CH(3)] of Met464, which is close to the C-lobe site, are quite distinct from those observed previously for Al(III), Fe(III), Ti(IV), Ga(III) and Bi(III) binding to hTF, suggesting that Zr(IV) binding may not induce lobe closure [as observed previously for Hf(IV)]. This may affect receptor recognition and play a role in the different biological behaviour of Zr(IV) compared to Ti(IV).
在存在次氮基三乙酸（NTA）、柠檬酸盐或乙二胺四乙酸（EDTA）作为供体配体的情况下，人血清脱铁转铁蛋白（hTF）与Zr(IV)的结合较为缓慢。以Zr(NTA)(2)(2-)作为供体时，在约2小时内达到平衡（pH 7.4，298 K，10 mM 4-(2-羟乙基)-1-哌嗪乙磺酸，5 mM碳酸氢盐），并且能够实现N端和C端位点的完全负载，从而得到Zr(2)-hTF。(13)C核磁共振数据表明，碳酸盐可以作为协同阴离子结合。(1)H和二维[(1)H,(13)C]（使用ε-[(13)C]甲硫氨酸-hTF）核磁共振研究表明，Zr(IV)摄取顺序中几乎没有叶选择性。Fe(III)首先从Zr(2)-hTF的C端取代Zr(IV)，随后是N端。然而，在大量过量NTA存在的情况下，Zr(IV)首先与全铁hTF（Fe(2)-hTF）的N端结合，随后是C端。靠近C端位点的甲硫氨酸464的ε-[(13)CH(3)]的(1)H和(13)C核磁共振化学位移变化与先前观察到的Al(III)、Fe(III)、Ti(IV)、Ga(III)和Bi(III)与hTF结合的情况有很大不同，这表明Zr(IV)结合可能不会诱导叶闭合[如先前对Hf(IV)所观察到的那样]。这可能会影响受体识别，并在Zr(IV)与Ti(IV)不同生物行为中发挥作用。
