The binding capacity of hen egg ovotransferrin (OVT) to different concentrations of iron ions was studied under multiple pH conditions and NaHCO3 concentrations. The effects of iron saturation on the thermal denaturation temperature and structure of OVT were analyzed by differential scanning calorimetry (DSC) and circular dichroism (CD) spectrum analysis. The results showed that complete iron saturation was obtained at an approximate iron ion to OVT molar ratio of 2.2. OVT exhibited higher iron-binding capacity under neutral or slightly alkaline pH conditions. The iron-binding capacity of OVT also increased with the increase in NaHCO3 concentration; however, a steady-state level was reached at NaHCO3 concentrations exceeding 75 mmol/L. The thermal denaturation temperature of OVT increased corresponding to the increase in iron saturation, and was observed to be 63.41 ℃ and 83.29 ℃ for apo-ovotransferrin (apo-OVT) and holo-ovotransferrin (holo-OVT), respectively. Apo-OVT showed a more negative band in the far-ultraviolet CD spectrum compared to holo-OVT; the α-helical content of apo-OVT decreased by 4.4%, while that of β-sheet strands, β-turns, and other structures increased by 2.80%, 1.20%, and 12.90%, respectively. The tertiary structure of holo-OVT displayed an obvious change in the near-ultraviolet region of the CD spectrum.
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