Interaction of curcumin with human serum albumin - A spectroscopic study

Curcumin (diferuloyl methane) has a wide range of physiological and pharmac ological actions. Curcumin interaction with human serum albumin (HSA) has b een followed by fluorescence quenching and circular dichroism (CD) measurem ents. Based on fluorescence measurements, the equilibrium constant for the interaction is 2.0 +/- 0.2 x 10(5) M-1. Binding of curcumin to HSA induces an extrinsic CD band in the visible region. From the induced CD band measur ements, the equilibrium constant has a value of 2.1 +/- 0.3 x 10(4) M-1. Th us, HSA has two kinds of affinity sites for curcumin, one with high affinit y and the other with lower affinity. Job's plot indicated a binding stoichi ometry of 1:1 for the high-affinity site. The equilibrium constant was inva riant with temperature in the range of 15 to 45 degrees C, suggesting the r ole of hydrophobic interactions in the binding of curcumin to HSA. Curcumin does not change the conformation of the HSA molecule. These measurements h ave implications in the understanding of the curcumin transport under physi ological conditions.