Iron Binding to Bovine Lactoferrin in Acidic Media (英文)

概要

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We investigated the binding of iron to bovine lactoferrin in the pH range 3.7-6.2. To study the effect of hydrogen ions on the binding sites, acetate buffer solutions were prepared to allow maintenance of a constant acetate ion concentration and ionic strength but variation of the hydrogen ion concentration. After addition of Fe (III) to the buffer solutions containing lactoferrin, absorption spectra were measured at 25℃ for solutions of different pH values. The results show that the absorbance at 465nm due to the Fe (III)-lactoferrin complex appears at pH 4.0 and increases with increasing pH but reaches a maximum at pH 6.0. From the molar ratio plot at this pH, the binding ratio of metal to protein is found to be 1:1. Using an estimated value of molar absorptivity, ε=2.2×10^3, the conditional formation constants at a given pH were evaluated. The pH dependence of the constants at pH 6-5 suggests a 1:1 competition between metal ions and hydrogen ions for the binding sites. Using the proton association constant of lactoferrin, log K=8.10, the formation constant of Fe (III)-lactoferrin complex was found to be log K=8.14.
2006-03-01