Role of phosphate-containing compounds in the transfer of indium-111 and gallium-67 from transferrin to ferritin.
Physiologic concentrations of ATP stimulate the translocation of gallium-67 (67Ga) from human transferrin (TF) to horse ferritin (HoFE). The mechanism of this translocation was examined. One millimolar ATP did not speed the binding of 67Ga or indium-111 (111In) to HoFE. ATP and pyrophosphate (PPi) at 1 mM, did not form high affinity complexes with 67Ga or 111In. ATP and PPi interacted directly with the [67Ga]TF complex and could within minutes increase the amount of nonprotein-bound 67Ga. Serum HCO3- concentration, 30 mM, prevented the ATP-induced dissociation of 67Ga from TF, whereas intracellular concentrations (0.4 and 5 mM) did not. Using a dialysis technique, ATP also stimulated the translocation of 111In from TF to HoFE; however, this process was much slower than with 67Ga. ATP caused an increase in the nonprotein-bound 111In compared to the control. These results suggest the formation of nonprotein-bound nuclide by these phosphate-containing compounds in a kinetically labile form is important to the translocation mechanism.
Weiner
R E
RE
Department of Radiology, Indiana University Medical Center, Indianapolis.
D000255:Adenosine Triphosphate; D000818:Animals; D001639:Bicarbonates; D001665:Binding Sites; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002845:Chromatography; D011756:Diphosphates; D004492:Edetic Acid; D005293:Ferritins; D005710:Gallium Radioisotopes; D006736:Horses; D006801:Humans; D007205:Indium Radioisotopes; D014168:Transferrin
D001639:Bicarbonates; D011756:Diphosphates; D005710:Gallium Radioisotopes; D007205:Indium Radioisotopes; D014168:Transferrin; D000255:Adenosine Triphosphate; D005293:Ferritins; D004492:Edetic Acid