Phelps C F, Antonini E
Biochem J. 1975 Jun;147(3):385-91. doi: 10.1042/bj1470385a.
The kinetics of iron and copper binding to hen's-egg apo-ovotransferrin were studied by using citrate chelates of these metals at pH9.3 in borate buffer in the presence of bicarbonate. The kinetics of the absorbance change associated with the formation of the final product show a fast process, which is pseudo-first-order, where the reagents are in excess with respect to the protein, and the citrate concentration is higher than 25mM. At lower citrate concentration, the progress curves are clearly biphasic. There is marked dependence of the rate of the reaction on bicarbonate concentration, which may be interpreted as a displacement reaction of the ligand-metal-protein ternary complex. The kinetics have been interpreted in the framework of a reaction scheme which involves bimolecular reaction of a metal chelate to the protein and subsequent colour development by displacement of the chelator by bicarbonate. The pH-dependence of this reaction supports the belief that tyrosine residues are involved in the process of iron-binding. The overall similarity of kinetics for iron and copper binding, notwithstanding their different co-ordination preferences, suggests that the process of metal-binding or chromophore development for the two metal complexes must be similar.
在pH9.3的硼酸盐缓冲液中，于碳酸氢盐存在的情况下，使用这些金属的柠檬酸盐螯合物研究了铁和铜与鸡卵脱铁转铁蛋白结合的动力学。与最终产物形成相关的吸光度变化动力学呈现出一个快速过程，该过程为准一级反应，此时相对于蛋白质而言试剂过量，且柠檬酸盐浓度高于25mM。在较低的柠檬酸盐浓度下，进程曲线明显呈双相。反应速率对碳酸氢盐浓度有显著依赖性，这可解释为配体 - 金属 - 蛋白质三元复合物的置换反应。该动力学已在一个反应方案的框架内得到解释，该方案涉及金属螯合物与蛋白质的双分子反应，随后通过碳酸氢盐置换螯合剂而显色。此反应的pH依赖性支持了酪氨酸残基参与铁结合过程的观点。尽管铁和铜具有不同的配位偏好，但它们结合动力学的总体相似性表明，两种金属络合物的金属结合或发色团形成过程必定相似。
