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

Abstract

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.