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Title: Selective, high-affinity binding of ferric ions by glycine-extended gastrin(17).
Austin Authors: Baldwin, Graham S;Curtain, C C;Sawyer, W H
Affiliation: University of Melbourne Department of Surgery, Austin Hospital, Melbourne, Victoria, Australia
Issue Date: 11-Sep-2001
Publication information: Biochemistry; 40(36): 10741-6
Abstract: Uptake of dietary iron is essential for replenishment of body stores. A role for the hormone gastrin in iron uptake as a chelator of ferric ions in the gastric lumen has been proposed previously [Baldwin, G. S. (1992) Med. Hypotheses 38, 70-74]. Here, spectroscopic evidence of selective, high-affinity binding of ferric ions to progastrin-derived peptides in aqueous solution at low pH is provided. The maximum at 281 nm in the absorption spectrum of glycine-extended gastrin(17) at pH 4.0 increased (2.07 +/- 0.30)-fold in the presence of > or =2 equiv of ferric ions. Titration of glycine-extended gastrin(17) with ferric ions under stoichiometric conditions indicated that the stoichiometry of binding was 2.00 +/- 0.28 mol of Fe(3+)/mol of peptide. Fluorescence quenching experiments yielded values for the stoichiometry and apparent dissociation constant of the ferric ion-glycine-extended gastrin(17) complex at pH 4.0 of 2.39 +/- 0.17 mol of Fe(3+)/mol and 0.62 +/- 0.19 microM, respectively. No interaction was detected with Co(2+), Cu(2+), Mn(2+), or Cr(3+). Electron paramagnetic resonance spectroscopy suggested that the iron ligands were either oxygen or sulfur atoms. Fluorescence quenching experiments with peptides derived from the glycine-extended gastrin(17) sequence indicated that one or more of the five glutamic acid residues were necessary for iron binding. The binding of ferric ions by glycine-extended gastrin(17) at low pH is consistent with a role for progastrin-derived peptides in iron uptake from the lumen of the gastrointestinal tract.
Gov't Doc #: 11535048
Type: Journal Article
Subjects: Binding Sites
Electron Spin Resonance Spectroscopy
Ferric Compounds.chemistry.metabolism
Gastric Mucosa.metabolism
Glutamic Acid
Hydrogen-Ion Concentration
Models, Biological
Protein Conformation
Spectrometry, Fluorescence
Appears in Collections:Journal articles

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