Abstract: The binding of Tb³⁺ to chicken apoovotransferrin was studied by monitoring the fluorescent intensity of Tb³⁺ at 549 nm. The conditional equilibrium constants for the complexation of Tb³⁺ by chicken apoovotransferrin in 0.1 mol/L hepes, at pH 7.4 and room temperature were measured. The successive macroscopic binding constants are lgK₁=9.08±0.12 and lgK₂=7.36±0.22. The molar fluorescence enhancement of Tb³⁺-apoovotransferrin complex is (2.06±0.14)×10⁴ mol^-1·L. The fluorescence quenching experiment and the titration of N-terminal monoferric ovotransferrin showed that Tb³⁺ has a preference for being bound to the N-terminal binding site of apoovotransferrin.

Key words: Terbium, Transferrin, Binding constant, Fluorescence