Tb(III) as a fluorescent probe for the structure of bovine serum albumin.

Tb(III) was used as a fluorescent probe in the study of the calcium-binding sites on Bovine Serum Albumin (BSA). The fluorescence of Tb(III) is enhanced markedly when bound to BSA and nonradiative energy transfer between two fluorescent tryptophan(Trp) residues and Tb(III) bound to calcium-binding sites on BSA occurred. Experimental results show that the major groups in BSA bound to metal ion are the carboxyl side groups of glutamic acid (Glu) and aspartic acid (Asp). The average distance between the bound Tb(III) and the two tryptophan residues in BSA calculated by a Föster dipole-dipole nonradiative energy transfer mechanism is 1.48 nm.