Comparative Study of Kinetic Parameters for Abstraction of Fe3+ from Monoferric (C- and N-terminal) and Diferric Forms of Bovine Lactoferrin by Acetohydroxamic Acid

Kinetic Study for Removal of Fe+3 from Metal Binding Sites

Abstract

This study reports the kinetic parameters for the removal of Fe3+ from both the metal binding sites of bovine lactoferrin by acetohydroxamic acid (AHA). The values of observed rate constants (kobs) were determined for iron removal from diferric, N- and C-terminals of monoferric lactoferrin under pseudo first-order conditions of [L] at pH values 7.5, 5.0 and 3.5. A saturation behavior for the dependence of kobs on ligand concentration at pH 7.5 was observed. At pH 5.0, both the monoferric forms show a saturation behavior with diferric lactoferrin following a combination of linear and saturation pathways. For a saturation pathway kobs are:

kmax [L]

kobs  =

where:

kd + [L]

[L] is the concentration of acetohydroxamic acid, kmax is the rate constant for the removal of iron at plateau, kd is ligand concentration required to reach half saturation.

While at pH 3.5, kobs follows: kobs = ko + k"' [L]

where:

k"' is the rate constant for iron abstraction from ferrilactoferrin through linear pathway, while ko is the rate constant for deferration of iron from ferrilactoferrin at lower pH and is independent of [L]. Moreover, the trends in the values of Kinetic parameters clearly show the inter-conversion of one type of pathway to another under varying conditions of pH.