The Dependence of the Copper Dissociation Rate Constants from Human(Serum)- and Ονο-Transferrin on pH and the Anions

Abstract Transferrin is an iron carrier protein. It is known that the conformational change in the protein moiety induced by binding of nonsynergistic anions influences the metal release rate constants from metal transferrins. The copper dissociation rate constants of dicupric human(serum)-transferrin and ovo-transferrin were measured under the conditions of various pHs and ionic strengths to estimate the residues which interact with nonsynergistic anions. The pH and the ionic strength dependence of the copper dissociation rate constants in the N-lobe of serum (human)-transferrin and both lobes of ovo-Tf clearly show that some residue which has a pKa around 6.0 is involved in the binding of nonsynergistic anions and accelerating the copper dissociation rate. In the C-lobe of serum(human)-Tf, the copper dissociation rate constants were almost independent of pH between pH 7.0 and 9.0, but the dissociation rates were constantly accelerated by the presence of 0.1 Μ KCl. This behavior suggests that the residue in the C-lobe of serum(human)-Tf is constantly protonated between pH 7.0 and 9.0 and is involved in the binding of nonsynergistic anions binding site.