Interaction Of Rare Earth Ions With Protein

Rare earth elements are used widely in industry, agriculture and medicine. It is inevitably that those elements entered the ecological environment, and access to animal and human body through the food chain. Proteins are material base of life, which are the carrier of many physiological functions and expresser of physiological characters. Therefor, it is important to study the mechanism of interaction between rare earth and proteins. The results maybe enable to provide a theoretical foundation for secure utilization of rare earth resources. The interaction between europium and three proteins, trypsin, hemoglobin and pepsin, as well as that of rare earth elements with glucose oxidase were investigated by cyclic voltammetry, UV/Vis absorption spectra and fluorescence spectra.Above all, the applications and the development of rare earth and the research progress of interaction of small molecules with proteins, as well as europium with proteins or enzymes were introduced briefly. The significance and contents of this paper were presented.Secondly, the redox properties of lanthanide chloride were discussed in pH7.4 buffer solution. Diffusion coefficient of Eu(III) in pH7.4 Tris-HCl buffer solution and pH2.0 HCl solution were calculated by Randles-Sevcik equation, respectively.From chapter three to chapter five, trypsin, hemoglobin and pepsin were chosen as models to investigate the interaction with Eu(III) in physiological pH conditions by electrochemical methods, UV/Vis absorption spectra and fluorescence spectra.Firstly, the redox properties of Eu(III) were determined in the presence of proteins at different concentrations. The electrochemical result showed that the interaction between proteins and Eu(III) led to the redox peak current of Eu(III) decreased. The reduction peak current decreased linearly with protein concentration. The fluorescence spectra indicate that presence of Eu(III) in solution led to the quenching of fluorescence of those three proteins. The quenching constant were calculated by the Stem-Volmer equation, which indicated the fluorescence quenching due to a rare earth-proein complex formed, and consist with static quenching mechanism. The number of binding site was close to 1 which obtained using Lineweaver-Burk linear equation and electrochemical method. UV-Vis absorption spectra revealed that the absorption at some peaks of trypsin, hemoglobin and pepsin changed and wavelength shifted to blue with the Eu(III) concentration increased. The results show that the addition of Eu(III) initiated the conformational change of proteins.In chapter six, nafion membrane was used for modified glucose oxidase on electrode surface. Cyclic voltammogram of modified electrodes were carried out in the buffer solution containing different concentrations of rare earth. With the addition of rare earth, the peak current of glucose oxidase decreased, and the separation between the potentials of the anodic and cathodic peaks increased. That means the irreversiblity of glucose oxidase reacted on electrode surface was decrease, which indicated that rare earth would change the conformation of the immobilized glucose oxidase. The results of fluorescence spectroscopy showed that the quenching of glucose oxidase fluorescence by rare earth was a static one which can be attributed to the formation of rare earth- glucose oxidase complex. The number of binding sites was calculated by Lineweaver-Burk linear equation.The mechanism of binding site of Eu(III) with protein was infered from interaction of Eu(III) with tryptophan discussed by cyclic voltammetry and fluorescence spectroscopy in chapter seven. The electrochemical result shows that Eu(III) reacted with tryptophan to form a complex. Eu(III) has a quite strong ability to quench the fluorescence launching of tryptophan, which indicate Eu(III) reacted with N of indole ring. The binding sites for Eu(III) with selected proteins were N of tryptophan indole ring.Chapter eight is the conclusion of full text.