Alpha-lactalbumin: A new carrier for vitamin D sub(3) food enrichment

Vitamin D is a fat-soluble regulatory vitamin maintaining blood calcium and phosphorus concentrations within a narrow physiological range. Binding to an appropriate delivery system can enhance vitamin D sub(3) solubility, simplify its transport, protect it from degradation and increase its bioavailability. Alpha-lactalbumin as a milk protein is a good candidate for a vitamin encapsulation. Binding properties and conformational change of bovine apo alpha-lactalbumin upon interaction with vitamin D sub(3) were investigated by calorimetry, spectroscopy and by molecular docking. Tryptophan fluorescence quenching indicates that the protein conformation changes in the presence of vitamin D sub(3). However, according to far UV CD results, the secondary structure of the protein was altered in the presence of vitamin D sub(3). The molecular modeling showed that Van der Waals interactions, hydrogen bond and hydrophobic interactions play a major role in the binding of vitamin D sub(3) to the alpha-lactalbumin hydrophobic pocket. The particle size of alpha-lactalbumin and vitamin D sub(3) complex is much larger than the native protein. Surprisingly, in the presence of vitamin D sub(3), the thermal stability of the protein decreases. The binding constant and standard Gibbs free energy change ( Delta G degree ) of binding vitamin D sub(3) to the protein obtained from ITC are 3.66 10 super(5) M super(-1) and -7.6 kcal mol super(-1), respectively, what agrees with results obtained by measurement of fluorescence and by molecular docking. The formed complex is a suitable candidate in order to enrich the low-fat food and non-alcohol drinks. According to the results, alpha-lactalbumin can be introduced suitable carrier for vitamin D sub(3).