title: The nonspecific binding of Fe3+ to transferrin in the absence of synergistic anions.
abstract: An obligatory role for barbonate (or other synergistic anions) in the specific binding of Fe3+ by transferrin has been a point of controversy for two decades. There are an equal number of confirmatory and negative reports of specific Fe3+-transferrin binary complexes. A criticism of previous studies is the use of only one synthetic route, and limited product testing. This study reports the development of several preparative routes aimed at the formation of a specific Fe3+-transferrin complex, and the characterization of the products by spectrophotometry and chemical reactivity. The preparative routes described include: (a) displacement of carbonate from Fe3+-transferrin-CO32- at low pH followed by removal of CO2 by several techniques; (b) addition of FeCl3 to apotransferrin under CO2-free conditions; (c) oxidation of Fe2+ in the presence of apotransferrin under CO2-free conditions; (d) reaction of apotransferrin with nonsubstituting Fe3+ complexes in the absence of CO2; and (e) attempts to displace anions from weak Fe3+-transferrin-anion complexes. The product were examined with regard to their visible spectra, and their examined with regard to their visible spectra, and their reactivity with: (a) NaHCO3, (b) Fe3+-nitrilotriacetic acid in NaHCO3, and (c) citrate. The results are compared with the characteristics of Fe3+-transferrin-anion complexes and nonspecific Fe3+, transferrin mixtures. The data indicate that in the absence of synergistic anions the affinity of the specific metal binding sites of transfe-rin for Fe3+ is so low as to not compete favorably with hydrolytic polymerization and nonspecific binding effects.
mesh_terms: D001639:Bicarbonates; D001665:Binding Sites; D002245:Carbon Dioxide / Q000494:pharmacology; D002254:Carbonates / Q000494:pharmacology; D002951:Citrates / Q000494:pharmacology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007501:Iron / Q000378:metabolism* / Q000494:pharmacology; D009571:Nitrilotriacetic Acid / Q000494:pharmacology; D011485:Protein Binding; D014168:Transferrin / Q000378:metabolism*
chemical_list: D001639:Bicarbonates; D002254:Carbonates; D002951:Citrates; D014168:Transferrin; D002245:Carbon Dioxide; D007501:Iron; D009571:Nitrilotriacetic Acid