Department of Chemistry and Biochemistry, Brigham Young University, Provo, UT 84602, USA.
Biometals. 2012 Apr;25(2):259-73. doi: 10.1007/s10534-011-9500-z. Epub 2011 Oct 20.
Ferritin iron loading was studied in the presence of physiological serum phosphate concentrations (1 mM), elevated serum concentrations (2-5 mM), and intracellular phosphate concentrations (10 mM). Experiments compared iron loading into homopolymers of H and L ferritin with horse spleen ferritin. Prior to studying the reactions with ferritin, a series of control reactions were performed to study the solution chemistry of Fe(2+) and phosphate. In the absence of ferritin, phosphate catalyzed Fe(2+) oxidation and formed soluble polymeric Fe(III)-phosphate complexes. The Fe(III)-phosphate complexes were characterized by electron microscopy and atomic force microscopy, which revealed spherical nanoparticles with diameters of 10-20 nm. The soluble Fe(III)-phosphate complexes also formed as competing reactions during iron loading into ferritin. Elemental analysis on ferritin samples separated from the Fe(III)-phosphate complexes showed that as the phosphate concentration increased, the iron loading into horse ferritin decreased. The composition of the mineral that does form inside horse ferritin has a higher iron/phosphate ratio (1:1) than ferritin purified from tissue (10:1). Phosphate significantly inhibited iron loading into L ferritin, due to the lack of the ferroxidase center in this homopolymer. Spectrophotometric assays of iron loading into H ferritin showed identical iron loading curves in the presence of phosphate, indicating that the ferroxidase center of H ferritin efficiently competes with phosphate for the binding and oxidation of Fe(2+). Additional studies demonstrated that H ferritin ferroxidase activity could be used to oxidize Fe(2+) and facilitate the transfer of the Fe(3+) into apo transferrin in the presence of phosphate.
在存在生理血清磷酸盐浓度（1mM）、升高的血清浓度（2-5mM）和细胞内磷酸盐浓度（10mM）的情况下，研究了铁蛋白的铁加载。实验比较了 H 和 L 铁蛋白同马脾铁蛋白的铁加载。在研究与铁蛋白的反应之前，进行了一系列对照反应以研究 Fe(2+)和磷酸盐的溶液化学。在没有铁蛋白的情况下，磷酸盐催化 Fe(2+)氧化并形成可溶的聚合 Fe(III)-磷酸盐络合物。Fe(III)-磷酸盐络合物通过电子显微镜和原子力显微镜进行了表征，结果显示出直径为 10-20nm 的球形纳米颗粒。可溶性 Fe(III)-磷酸盐络合物也作为铁加载到铁蛋白中的竞争反应形成。从 Fe(III)-磷酸盐络合物中分离出的铁蛋白样品的元素分析表明，随着磷酸盐浓度的增加，马铁蛋白的铁加载量减少。在马铁蛋白中形成的矿物质的组成具有更高的铁/磷酸盐比（1:1），而从组织中纯化的铁蛋白的铁/磷酸盐比（10:1）更高。由于这种同聚物中缺乏亚铁氧化酶中心，磷酸盐显著抑制了 L 铁蛋白的铁加载。分光光度法测定 H 铁蛋白的铁加载显示在磷酸盐存在下具有相同的铁加载曲线，表明 H 铁蛋白的亚铁氧化酶中心能够有效地与磷酸盐竞争结合和氧化 Fe(2+)。进一步的研究表明，在磷酸盐存在下，H 铁蛋白的亚铁氧化酶活性可以用于氧化 Fe(2+)并促进 Fe(3+)向脱铁转铁蛋白的转移。
