The interaction of ¹²⁵I-labelled various species of transferrin including Ga_C-Tf, Ga₂-Tf and Ga_C-Tf-Fe_N with HL60 cells was investigated. The results showed that the proteins bound to membrane of cells at pH＝7.4 and 0 ℃. The association constants were (1.2±0.14)×10⁸, (1.1±0.19)×10⁸ and (1.8±0.42)×10⁸ L/mol for Ga_C-Tf, Ga₂-Tf and Ga_C-Tf-Fe_N, respectively. At the same time, the association constant for ¹²⁵I-labelled apotransferrin was (0.97±0.20)×10⁸ L/mol. There were about (4.8±0.11)×10⁵ transferrin receptors per cell surface. In vitro studies indicated that com-plexes of Ga and transferrin bind to transferrin receptor with the order of apoTf≈Ga_C-Tf≈Ga₂-Tf＜Ga_C-Tf-Fe_N in terms of their association constants.

Key words: transferrin, gallium(III), ¹²⁵I-labeling, HL60 cells