Interactions between sodium oleate and α-lactalbumin: The effect of temperature and concentration on complex formation

Complexes of α-lactalbumin and oleic acid have previously been shown to be cytotoxic to cancer cells. In this study oleic acid is replaced by the more soluble sodium oleate and complexes of α-lactalbumin and sodium oleate are formed. Dynamic light scattering results showed that there was a small linear increase in the particle size of α-lactalbumin when it was titrated with sodium oleate. The fluorescence spectra of α-lactalbumin showed a linear increase in the emission maximum when sodium oleate was added up to a molar ratio of 8–11 oleate molecules per α-lactalbumin. Differential scanning calorimetry results show that the thermal unfolding of α-lactalbumin is altered by the presence of the sodium oleate. There is a decrease in size of the endothermic peak of apo α-lactalbumin when sodium oleate is added. The temperature at which unfolding occurred decreased for both apo and holo α-lactalbumin. FTIR measurements showed no significant effect of sodium oleate in the amide I region of the α-lactalbumin spectrum indicating the presence of oleate has little or no effect on the secondary structure of α-lactalbumin. The interactions between α-lactalbumin and sodium oleate/oleic acid are pH dependent, turbidity and dynamic light scattering measurements showed that the association between the two was optimal between pH 6.0 and 8.0.The results obtained here suggest that α-lactalbumin can bind at least a 20 fold molar excess of oleate, most likely in a non-specific manner.

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