Proton Relaxation Times in Protein Complexes of Paramagnetic Ions

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Abstract
Proton longitudinal relaxation times in dilute solutions of Fe3+, iron conalbumin (FeCon), and ferrihemoglobin (Hb+), have been measured at 40 and 60 Mc. The static magnetic moment is 5.9 Bohr magnetons for all three species; the ratios of 1/NT1 for Fe3+, Fe Con, and Hb+ are 1:0.72:0.026. For the proteins the relevant correlation time τc in Solomon's expression for the dipolar contribution to T1 is the electron spin relaxation time τS of the paramagnetic ion, which for Fe Con is 3×10—11 sec. τS may contribute to τc in other complexes of Fe3+ and Cr3+. A simple model for Hb+ shows the heme Fe to be 4 A from the surface of the protein.

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