The Denaturation of Lactoferrin and Transferrin by Urea

Lactoferrin and transferrin were submitted in their metal‐free forms as well as in their ironsaturated forms to various concentrations of urea, in the presence or absence of 2‐mercaptoethanol. The progressive unfolding of the proteins was followed by their optical activity in the visible region. The change in the three‐dimensional structure of lactoferrin when binding iron was found to be more profound than in transferrin whose stability is more dependent on disulphide bridges. In the absence of 2‐mercaptoethanol, the concentrations of urea which caused 50% denaturation at pH 7.4 were found to be respectively 4 M for apolactoferrin, 4.9 M for apotransferrin, 5.5 M for Fe·transferrin and 8 M for Fe·lactoferrin. In the presence of 2‐mercaptoethanol, these values became respectively 2 M for apotransferrin, 2.5 M for apolactoferrin, 3.9 M for Fe·transferrin and 6.7 M for Fe·lactoferrin. The loss of iron‐binding ability, estimated from absorbance at 460 nm, was found to follow strictly the evolution of the [m']546 parameter.