Abstract
The effects of anions on the thermostability of ovotransferrin (oTf) were investigated. The temperature, Tm, causing aggregation of oTf was measured in the presence or absence of anions, and the denaturation temperature, TmDSC, was also determined by differential scanning calorimetry (DSC) in the presence of the citrate anion. We found that some anions (phosphate, sulfate and citrate) raised temperature Tm of oTf by about 5–7 °C. However, neither sodium chloride nor sodium bicarbonate raised Tm by that much. Temperature Tm was increased by increasing the concentration of the citrate anion, and was in good agreement with denaturation temperature TmDSC, suggesting that denaturation of the oTf molecules resulted in aggregation of oTf. We also demonstrated that the anions, especially sulfate, repressed the heat-aggregation of liquid egg white.
The Van’t Hoff plot from the Tm and ΔHd values revealed that two anion-binding sites were concerned with heat stabilization. These binding sites may have been concerned with sulfate binding (not bicarbonate binding) that is found in the crystal structure of apo-form of oTf, since the bicarbonate anion did not raise Tm.
