Thermal Denaturation of Human Lactoferrin and Its Effect on the Ability to Bind Iron

Thermal stability of human milk lactoferrin was studied by differential scanning calorimetry and compared with that of recombinant human lactoferrin produced in Aspergillus awamori. Maximum peak temperature, transition enthalpy, and activation energy of lactoferrin as isolated from human milk (67.0°C, 2276 kJ/mol, and 275.5 kJ/mol, respectively) increased significantly when lactoferrin was fully saturated with iron (90.6°C, 3209 kJ/mol, and 387.6 kJ/mol, respectively) which indicates that the binding of iron to lactoferrin is an important factor in the stabilization of its structure. Similar results were obtained for recombinant human lactoferrin, indicating a high degree of resemblance between both proteins. The ability of human lactoferrin to bind iron after heat treatment was also studied, remaining practically intact after treatments of 72°C for 20 s or 135°C for 8 s, while more severe treatments reduced markedly this ability.