Reductive release of Fe(III) from Bovine Lactoferrin by Ascorbic Acid

Abstract

The kinetics of the reduction of Fe3+ from bovine diferric Lactoferrin (Fe2Lf) and monoferric C-terminal (FeC-Lf) and N-terminal (Lf-FeN) sites is investigated at pH 6.1 and 3.5 under pseudo first-order conditions using ascorbic acid (AA) as a biological reducing agent and 1, 10- Orthophenanthroline (O-phen) as Fe2+ chelator. Pseudo first-order rate constants as a function of ascorbic acid concentration are measured. Second order rate constants (k2) for Fe2Lf, Lf-FeN, FeC-Lf at pH 6.1 and 27 ° C are 0.1527 M-1.min-1, 0.0381 M-1.min-1, 0.1381 M-1.min-1, respectively. While, at pH 3.5 and 27 ° C these values are 0.1915 M-1.min-1, 0.1116 M-1.min-1, 0.4434 M-1.min-1, respectively. A linear dependence of kobs on ascorbic acid concentration is suggestive of simple pseudo first-order pathway for reduction of iron under the conditions applied for all the three forms of protein. Moreover, the results show that the C-terminal site is more labile toward reduction by ascorbic acid than the N-terminal site.