铕(Ⅲ)离子与人血清脱铁转铁蛋白结合的紫外差光谱研究

UV Difference Spectra Study on the Binding of Europium Ion with Apotransferrin

在pH7.4,温度为25℃的条件下,用紫外吸收差光谱进行了Eu^(3+)对人血清脱铁转铁蛋白的滴定.结果表明Eu^(3+)与人血清脱铁转铁蛋白结合后其差光谱在245nm和296nm处出现吸收峰,在245nm处,Eu^(3+)-脱铁转铁蛋白配合物的摩尔吸光系数是(2.2±0.1)×10~4cm^(-1)·mol^(-1)·dm^3,Eu^(3+)可占据脱铁转铁蛋白的2个金属离子结合部位,Eu^(3+)优先占据脱铁转铁蛋白的C端结合部位,条件平衡常数是logK_c=8.42±0.12,logK_N=6.03±0.42.Eu^(3+)与R_E^(3+)(R_E=Nd,Sm,Gd和Tb)间的线性自由能关系表明,稀土离子占据脱铁转铁蛋白的C端结合部位时受离子大小的影响.

The binding of Eu3+ to human serum apolransferrin has been studied by monitoring the change of difference UV spectra at 245nm. Conditional equilibrium constants for the complexation of Eu3+ byhuman serum apotransferrin in 0.1 mol·dm-3 hepes, pH 7.4, at 25℃ have been measured. The results arelogKc = 8.42±0. 12 and logKN =6.03±0.42 for complexation of Eu3+ .The molar absorptivity perbinding site for Eu3+ is (2. 2 ±0. 1) × 104cm-1·mol-1·dm3. Titration of both C and N terminal monoferric transferrins with Eu3+ indicate that Eu3+ binding is stronger at the C terminal binding site than the N terminal binding site. Linear free energy relationships for Eu3+ and RE3+ (RE = Nd, Sm, Gd and Tb) have been established. There is a size restriction for the binding of lanthanide ions on C terminal binding site of apotransferrin.