Study of the binding of Eu3+ and Tb3+ to L-phenylalanine and L-tryptophan

Journal of the Brazilian Chemical Society

Massabni, Ana M. G.¹  Leite, Sergio R. de A.¹  Carubelli, Célia R.¹ 

关键词: aromatic amino acids;    lanthanides;   

DOI  :  10.1590/S0103-50531997000600006

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

About a third of all proteins in their native state contain bound metal ions, or require metal ions for a variety of metabolic pathways1. In many cases, Ca2+ either constitutes protein metal center or is needed for cell biological activity. This metal ion exhibits no satisfactory spectroscopic properties, so the study of calcium depending proteins by spectroscopic techniques is extremely difficult. To overcome this problem, it is often possible to substitute a trivalent lanthanide (Ln3+) for Ca2+ ions within those proteins. No serious structural changes or loss of specific functions are observed after such substitution. Among the lanthanide ions, Tb3+ and Eu3+ generally show luminescent emission that is enhanced when these ions are bound to a protein. The luminescence excitation may be performed by irradiation in the range of aromatic spectral absorption bands. As a rule, tryptophan is responsible for energy transfer to Ln3+ ions, although tyrosine and phenylalanine may be involved in this process2. So, it seems profitable, in view of eventual biochemical and biophysical applications, to study the interaction between aromatic amino acids and lanthanide ions, whose luminescence may be considered as specific to prove their presence. No paper has been published on this issue in recent years. The last work published is that by Aizawa et al., in 1987, where the interaction of tryphophan with Tb3+ ions had been studied using fluorescence and 1H-NMR spectroscopies3. These authors had concluded that terbium interacts with a-amino and imine groups, the latter belonging to the indole ring. No interaction with the carboxylate group was reported. Such conclusions, based mainly on the 1H-NMR measurements, seem unconvincing, since they are in contradiction with the coordination chemistry of the lanthanides. These hard acids according to Pearsons theory4, should interact more strongly with oxygen than with nitrogen. Especially when the latter has a positive charge, this being the

【 授权许可】

Unknown