title: Electron paramagnetic resonance measurement of the distance between the metal binding sites of transferrin.
abstract: The distance between the two metal binding sites of human serum transferrin is calculated from measurements made of the paramagnetic broadening of the EPR spectrum of Cu2+ bound at the NH2-terminal (B) site from Fe3+ bound at the COOH-terminal (A) site. Complexes of monoferric(A)-monocupric(B) transferrin, monocupric(B) transferrin, and monogallium(A)-monocupric(B) transferrin were prepared under identical conditions. Computer simulation and direct measurement of the EPR spectra from these complexes demonstrate a paramagnetic broadening of 0.6 +/- 0.1 G in the line width of the Cu2+ spectrum due to the paramagnetic Fe3+ bound at the other site. The distance between the two metal binding sites is calculated to be 41.6 +/- 2.8 A.
mesh_terms: D001665:Binding Sites; D003300:Copper / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D006801:Humans; D007501:Iron / Q000378:metabolism*; D007700:Kinetics; D011485:Protein Binding; D011487:Protein Conformation; D014168:Transferrin / Q000378:metabolism*
chemical_list: D014168:Transferrin; D003300:Copper; D007501:Iron