Interaction of curcumin with human serum albumin--a spectroscopic study.

Curcumin (diferuloyl methane) has a wide range of physiological and pharmacological actions. Curcumin interaction with human serum albumin (HSA) has been followed by fluorescence quenching and circular dichroism (CD) measurements. Based on fluorescence measurements, the equilibrium constant for the interaction is 2.0+/-0.2x10(5) M(-1). Binding of curcumin to HSA induces an extrinsic CD band in the visible region. From the induced CD band measurements, the equilibrium constant has a value of 2.1+/-0.3x10(4) M(-1). Thus, HSA has two kinds of affinity sites for curcumin, one with high affinity and the other with lower affinity. Job's plot indicated a binding stoichiometry of 1:1 for the high-affinity site. The equilibrium constant was invariant with temperature in the range of 15 to 45 degrees C, suggesting the role of hydrophobic interactions in the binding of curcumin to HSA. Curcumin does not change the conformation of the HSA molecule. These measurements have implications in the understanding of the curcumin transport under physiological conditions.