Reductive release of Fe(III) from bovine lactoferrin by ascorbic acid

The kinetics of the reduction of Fe/sup 3+/ from bovine diferric Lactoferrin (Fe/sub 2/Lf) and monoferric C-terminal (Fe/sub C/-Lf) and N-terminal (Lf-Fe/sub N/) 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-Ortho phenanthroline (O-phen) as Fe/sup 2+/ chelator. Pseudo first-order rate constants as a function of ascorbic acid concentration are measured. Second order rate constants (k2) for Fe/sub 2/Lf, Lf-Fe/sub N/, Fe/sub C/-Lf at ph 6.1 and 27 deg. C are 0.1527 M/sup -1/.min/sup -1/, 0.0381 M/sup -1/.min-1, 0.1381 M/sup -1/.min/sup -1/, respectively. While, at ph 3.5 and 27 deg. C these values are 0.1915 M/sup -1/.min-1, 0.1116 M/sup -1/.min/sup -1/, 0.4434 M/sup -/.min/sup -1/, respectively. A linear dependence of k/sub obs/ 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. (author)