title: Differed preferential iron-binding lobe in human transferrin depending on the presence of bicarbonate detected by HPLC/high-resolution inductively coupled plasma mass spectrometry.
abstract: The binding of iron (Fe) to human serum transferrin (Tf) was analyzed with an HPLC system equipped with an anion exchange column and directly connected with a high-resolution inductively coupled plasma mass spectrometer for metal detection. The (56)Fe level in the eluate was monitored at resolution m/Deltam=3000. Two monoferric Tfs were assigned based on the results of urea-PAGE and desferrioxamine experiments. When Fe was added as Fe-citrate stepwise to an apo-Tf solution in the presence of bicarbonate, the N-lobe site was the preferential Fe-binding site, while the C-lobe site was preferred in the absence of bicarbonate. In both cases, the Fe-peak areas of the preferential site and Fe(2)-Tf increased up to an Fe/Tf molar ratio of 1, and then the peak area of the monoferric Tf decreased while the peak area of Fe(2)-Tf increased. When the Fe/Tf molar ratio was below 1, the amount of Fe bound to the lobe with a weaker affinity was higher in Fe(2)-Tf than in the monoferric Tf in each case. Namely, Fe(2)-Tf was the preferential binding state of Fe to human serum Tf. The preference is reasonable for transferring Fe ions effectively to Tf-receptors.
authors.affiliation: National Institute of Health Sciences, Kamiyoga 1-18-1, Setagaya, 158-8501, Tokyo, Japan.
authors.forename: M H
authors.initials: MH
authors.lastname: Nagaoka
authors.forename: T
authors.initials: T
authors.lastname: Maitani
mesh_terms: D001059:Apoproteins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D002851:Chromatography, High Pressure Liquid; D006801:Humans; D007501:Iron / Q000378:metabolism*; D013058:Mass Spectrometry; D017693:Sodium Bicarbonate / Q000494:pharmacology*; D014168:Transferrin / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D001059:Apoproteins; D014168:Transferrin; C028284:apotransferrin; D017693:Sodium Bicarbonate; D007501:Iron