A comparison of effects of pH on the thermal stability and conformation of caprine and bovine lactoferrin

Thermal stability and structural changes in caprine lactoferrin (cLF) and bovine lactoferrin (bLF) at pH 2.0–8.0 were measured using thermal denaturation temperature (Tm) analysis, fluorescence spectroscopy and circular dichroism (CD). Thermal stability analysis indicated a Tm of 70 °C for bLF and 67 °C for cLF at pH 7.0. From pH 7.0 to 3.0, a gradual reduction in the Tm of both bLF and cLF was observed and reached a value of 39 °C and 30 °C, respectively. At pH 2.0–3.0, a partly unfolded structure of bLF and cLF was observed with a relatively low content of α-helix structure (3% and 7%, respectively), but still rich in β-structure (54% and 57%, respectively). A higher exposure of hydrophobic surfaces at low pH for bLF compared with cLF was proved by fluorescence studies. In conclusion, the structure of cLF was more affected by pH and showed lower temperature stability than bLF.