Magnetic resonance studies of Mn(II)-, Mn(III)-, and Fe(III)-conalbumin complexes

✍ Scribed by Joseph J. Villafranca; Raj P. Pillai; Robert C. Woodworth

• Publisher: Elsevier Science
• Year: 1976
• Weight: 688 KB
• Volume: 6
• Category: Article
• ISSN: 0006-3061
• DOI: 10.1016/s0006-3061(00)80230-6

✦ Synopsis

Apoconalbumin binds _Mn(II) at two sites with association constants of K1 = 7(%1) x lo4 and Kz = 0.4(?0.25) x lo4 M-l. The binding is tighter in the presence of excess bicarbonate resulting in K1 = l-8(*0.2) X lo5 and K2 = 3(+2) X IO4 M-l. The electron paramagnetic resonance spectrum (at both 9 and 35 GHz) of Mn(II) bound at the ti&t site reveals a rhombic distortion (A = E/D s 0.2.5-0.31) in the protein l&and environment of the metal ion_ An evaluation of the l/pTIP. p aramagnetic contribution to the longitudinal relaxation rate of solvent protons with Mn(Il)-. Mn(III)-, and Fe(III)derivatives of conalbumin revealed that the metal ion in each site of conalbumin is accessiile to one water molecule_ For Mn(II)-conaIbumin and Mn(III)conalbumin species, inner coordination sphere protons are rapidly eschanging with the bulk solvent, while slow exchange conditions prevail for Fe(III)conalbumin.