Interaction of αS1-Casein with Curcumin and Its Biological Implications

alpha(S1)-Casein is one of the major protein components of the casein fraction of milk. Curcumin (diferuloyl methane), the major curcuminoid, constituting about 2-5% of turmeric (Curcuma longa) is the active ingredient with many physiological, biochemical, and pharmacological properties. On the basis of spectroscopic measurements, it is inferred that curcumin binds to alpha(S1)-casein at pH 7.4 and 27 degrees C with two binding sites, one with high affinity [(2.01 +/- 0.6) x 10(6) M-1] and the other with low affinity [(6.3 +/- 0.4) x 10(4) M-1]. Binding of curcumin to alpha(S1)-casein is predominantly hydrophobic in nature. The anisotropy of curcumin or conformation of alpha(S1)-casein did not change on interaction. The stability of curcumin in solution at pH 7.2 was enhanced on binding with alpha(S1)-casein. The chaperone-like activity of alpha(S1)-casein gets slightly enhanced on its binding to curcumin. The ability of curcumin to protect erythrocytes against hemolysis was not affected due to curcumin- alpha(S1)-casein interaction. The two binding sites of alpha(S1)-casein for curcumin, along with enhanced solution stability on interaction, may offer an alternative approach in physiological and nutritional applications.