Studies On The Binding Of Iron,aluminum And Heavy Rare Earth Ions To Apotransferrin By Fluorescence And Ultraviolot Spectra

The study of interaction between metal ions and proteins is a new frontier of chemistry and life science. Transferrin (Tf) is a large class of genetic correlation, basic structure and biological function similar to the iron-binding protein, having different classifications in accordance with different standards.Transferrin (Tf) is a combination of non-heme iron glycoprotein.Each transferrin molecule has two ferric ion binding sites. The main function of transferrin is combing free ferric irons, so that ferric ions can become soluble and absorbent state by cells. About transferrin-mediated ferric ions'absorption , Scientific workers have already made a substantial amount of research work. The main way that ferric ions being absorpted by cell is through the transferrin-bound,it leads to the conformational change which mades transferrin easily combining to transferrin receptor (TfR), forming a composite, and then endosome forming endocytosis body. Endocytosis body in the acidic environment make transferrin releasing iron. At that moment, the heme iron can be used as protein, the ribosome nucleotide reductase cofactors or stored in the iron protein.In normal human plasma the concentration of ferric ion is the 10-30μmol/L (mean 20μmol/L), while the concentration of Tf is 22-35μmol/L (mean 30μmol/L). Each Tf molecule can binds two ferric irons,so that the normal human plasma Tf is only 30(20-50)% saturated by ferric irons,and about 70% of the binding sites are empty. Empty binding sites can combine the other metal ions in human blood.With the growing application of rare earth(RE), a growing number of them enter into the environment, into the food chain. The biological effects of rare earth and human health effects have arose more and more concern and attention.Studys have found that the normal growth of plants need rare earth; RE may be the regulator of animals body functions. Light rare earth elements (LREE) such as La³⁺,Ce³⁺,Pr³⁺,Nd³⁺,Sm³⁺,Eu³⁺ have obvious role in promoting on the growth of plants and animals.Heavy rare earth elements (HREE) such as Tm³⁺, Yb³⁺ have certain stimulation to the promotion, but when their concentration is large,they show the toxic effect. Research on rare earth ions and transferrin molecule for the combination of rare earth ions on the biological effects is of great significance.Through massive experiments we found: If Tf combines with Fe³⁺and Al³⁺, its fluorescence will be quenched. Using this phenomenon we investigate the combination of Tf with Fe³⁺ and Al³⁺quantitatively, concluded that each Tf molecule have two binding sites with Fe³⁺and Al³⁺; Further, we have researched the competition between Tf and complexing agent (EDTA) with Fe³⁺ by fluorescence quenching method;In the meantime we have also researched the competition between Al³⁺, Fe³⁺and In³⁺ with Tf. The results show the binding order through the size of their constants. The results gained through researching the binding between Tf and Fe³⁺,Al³⁺ by UV difference spectroscopy verified conclusion using fluorescence quenching method.Below we focus researching the combination between Tf and several heavy rare earth ions (Dy³⁺, Er³⁺, Tm³⁺, Lu³⁺) by UV difference spectroscopy. These heavy rare earth ions can combine with the transferrin, causing the same conformational changes. However, the conformational change arising from heavy rare earth ions is different from that arising from Fe³⁺ and Al³⁺. The main differents is that the conformational change caused by binging heavy rare earth ions has greatly varied at start-up phase, then conformational change of Tf has became smoothly.Through the above study it helps us to understand the interaction between metal ions and biological macromolecules. It is of great significance for the study of the biological effects of rare earth ions. This study methods and discussion in this article will have certain reference value on other research fields such as Biochemistry, Analytical Chemistry,etc.