Electron spin echo envelope modulation evidence for carbonate binding to iron(III) and copper(II) transferrin and lactoferrin.
Iron binding to transferrin and lactoferrin requires a synergistic anion, which is carbonate in vivo. The anion is thought to play a key role in iron binding and release. To understand better the iron-carbonate interaction, experiments were performed with iron(III) and copper(II) complexes of human milk lactoferrin and serum transferrin with carbon-13-labeled carbonate. Modulation frequencies were present in the Fourier transforms of two-pulse and three-pulse electron spin echo envelope modulation data for the Fe(III) and Cu(II) complexes, consistent with binding of carbonate to both metals. The metal-13C interaction was similar for the lactoferrin and transferrin complexes. Spin coupling to the nitrogen of a coordinated histidine imidazole was observed for both metals. Both the metal-nitrogen and the metal-carbon spin coupling constants were about a factor of 5 smaller for the iron complexes than for the copper complexes, which indicated substantial similarity in the metal-carbonate and metal-imidazole binding for the two metals.
Eaton
S S
SS
Department of Chemistry, University of Colorado, Denver 80204.
Dubach
J
J
Eaton
G R
GR
Thurman
G
G
Ambruso
D R
DR
D002254:Carbonates / Q000378:metabolism*; D003300:Copper / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy / Q000379:methods; D005260:Female; D005583:Fourier Analysis; D006801:Humans; D007501:Iron / Q000378:metabolism*; D007781:Lactoferrin / Q000378:metabolism*; D007782:Lactoglobulins / Q000378:metabolism*; D008895:Milk, Human / Q000378:metabolism; D011485:Protein Binding; D014168:Transferrin / Q000378:metabolism*
D002254:Carbonates; D007782:Lactoglobulins; D014168:Transferrin; D003300:Copper; D007501:Iron; D007781:Lactoferrin