Doctor of Philosophy
Date of Defense
Wesley Harris, PhD.
Transferrin, the serum iron transport protein in humans, is used to transport 30-40 mg of iron per day through blood. The accessibility of transferrin makes it an attractive target for iron cheating therapeutic agents used in the treatment of iron overload. There is an ongoing search for ligands which can accelerate the rate of iron release, as the currently approved drug DFO has a very slow rate for iron removal. Previous studies have shown that anions can accelerate the rate of iron release. Studies on the effect of anions on the rates of iron release from C-terminal monoferric transferrin at pH 7.4 have been conducted using the ligands acetohydroxamic acid (AHA) and 1,2-dimethyl-3-hydroxy-pyridinone (L1), which follow saturation kinetics, and the ligands, nitrilotriacetic acid (NTA) and diethylenetriaminepentaacetic acid (DTPA), which follow first order kinetics with respect to the ligand concentration. The effects of sulfonates, phosphonates and phosphonocarboxylates have been studied. The anions are divided into two types, simple (non-coordinating) and complex (capable of chelating iron). The simple anions accelerate the rate of iron release, presumably by binding to an allosteric anion binding site on the transferrin. This binding increase the value of kmax for the saturation pathway for AHA and L1 and introduces a kmax for NTA, which otherwise does not have a saturation component. This changes the kinetic behavior of NTA from a strictly first-order dependence on the ligand concentration to complex kinetics, a combination of saturation and first-order kinetics. The complex anions, which can also chelate iron, decrease the rate of iron release by the reference ligands. These anions can also generate a small first order component for iron removal by ligands that normally follow saturation kinetics. These studies emphasize that the appearance of the first order component is due to the replacement of synergistic anion by the incoming chelating ligand and is not an allosteric effect of the anionic ligand. Distinct effects of anions on the saturation and first-order components for iron release are reported. For NTA, the major impact of anions is a decrease in the value of k’.
Sharma, Rashmi Subhash Chander, "Effect of Anions on the Iron Release Pathways of Human Serum Transferrin" (2010). Dissertations. 483.