Anion-mediated Iron Release from Transferrins: The Kinetic And Mechanistic Model For N-Lobe Of Ovotransferrin

Muralidhara, B. K. and Hirose, Masaaki (2000) Anion-mediated Iron Release from Transferrins: The Kinetic And Mechanistic Model For N-Lobe Of Ovotransferrin. Journal of Biological Chemistry, 275 (17). pp. 12463-12469.

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Abstract

Iron release process of ovotransferrin N-lobe (N-oTf) to anion/chelators has been resolved using kinetic and mechanistic approach. The iron release kinetics of N-oTf were measured at the endosomal pH of 5.6 with three different anions such as nitrilotriacetate, pyrophosphate, and sulfate using stopped flow spectrofluorimetric method, all yielding clear biphasic progress curves. The two observed rate constants and the corresponding amplitudes obtained from the double exponential curve fit to the biphasic curves varied depending on the type and concentration of anions. Several possible models for the iron release kinetic mechanism were examined on the basis of a newly introduced quantitative equation. Results from the curve fitting analyses were consistent with a dual pathway mechanism that includes the competitive iron release from two different protein states, namely, X and Y, with the respective first order rate constants of K1 and K2 (X, domain closed holo N-oTf; Y, anion induced different conformer of holo N-oTf). The reversible interconversions of X to Y and Y to X are driven by the second order rate constant k3 and the first order rate constant K4, respectively. The obtained rate constants were greatly variable for the three anions depending on the synergistic or nonsynergistic nature. In the light of the anion-binding sites of N-oTf located crystallographically, the compatible mechanistic model that includes competitive anion binding to the iron coordination sites and to a specific anion site is suggested for the dual pathway iron release mechanism.

Item Type:	Article
Uncontrolled Keywords:	ovotransferrin N-lobe Iron release Transferrins
Subjects:	500 Natural Sciences and Mathematics > 04 Chemistry and Allied Sciences > 29 Protein Chemistry
Divisions:	Protein Chemistry and Technology
Depositing User:	Food Sci. & Technol. Information Services
Date Deposited:	09 Jan 2008 07:33
Last Modified:	28 Dec 2011 09:32
URI:	http://ir.cftri.res.in/id/eprint/1623

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