Transferrins: iron release from lactoferrin

Iron loss in vitro by the iron scavenger bovine lactoferrin was investigated in acidic media in the presence of three different monoanions (NO 3 −, Cl − and Br −) and one dianion (SO 4 2−). Holo and monoferric C-site lactoferrins lose iron in acidic media (pH⩽3.5) by a four-step mechanism. The first two steps describe modifications in the conformation affecting the whole protein, which occur also with apolactoferrin. These two processes are independent of iron load and are followed by a third step consisting of the gain of two protons. This third step is kinetically controlled by the interaction with two Cl −, Br − and NO 3 − or one SO 4 2−. In the fourth step, iron loss is under the kinetic control of a slow gain of two protons; third-order rate-constants k 2, 4.3(±0.2)×10 3, 3.4(±0.5)×10 3, 3.3(±0.5)×10 3 and 1.5(±0.5)×10 3 M −2 s −1 when the protein is in interaction with SO 4 2−, NO 3 −, Cl − or Br −, respectively. This step is accompanied by the loss of the interaction with the anions; equilibrium constant K 2, 20±5 mM, 1.0(±0.2)×10 −1, 1.5(±0.5)×10 −1 and 1.0(±0.3)×10 −1 M 2, for SO 4 −, NO 3 −, Cl − and Br −, respectively. This mechanism is very different from that determined in mildly acidic media at low ionic strength (μ