Kinetics of the removal of ferric ion from transferrin by aminoalkylphosphonic acids

Abstract

The kinetics of ion removal at 25°C in 0.1 M Tris, pH 7.4 by a series of phosphonic acids have been evaluated. The initial rate of iron removal is first order in ferric-transferrin, but shows a hyperbolic dependence on the concentration of the phosphonate ligand. At high ligand concentrations the reaction is clearly biphasic, and the data are interpreted in terms of nonequivalent rate constants for iron removal from the two transferrin iron-binding sites. Rate constants for three phosphonic acid ligands are $ ̃ 0.025 min −1 and $ ̃ 0.007 min −1 for the faster and slower binding sites. The results are discussed in relation to the conformational change mechanism for iron removal from transferrin proposed by Cowart et al. [21].