Interaction of nobiletin with human serum albumin studied using optical spectroscopy and molecular modeling methods

The binding of nobiletin to human serum albumin (HSA) was investigated by fluorescence, UV-vis, FT-IR, CD, and molecular modeling. Fluorescence data revealed the presence of a single class of binding site on HSA and its binding constants (K) at four different temperatures (289, 296, 303 and 310 K) were 4.054, 4.769, 5.646 and 7.044 x 10(4)M(-1), respectively. The enthalpy change (Delta H-0) and the entropy changes (Delta S-0) were calculated to be 1.938 kJ mol(-1) and 155.195J mol(-1) K-1 according to the Van't Hoff equation. The binding average distance, r, between the donor (HSA) and the acceptor (nobiletin) was evaluated and found to be 2.33 mn according to the Forster's theory of non-radiation energy transfer. Changes in the CD and FT-IR spectra were observed upon ligand binding along with a significant degree of tryptophan fluorescence quenching on complex formation. Computational mapping of the possible binding sites of nobiletin revealed the molecule to be bound in the large hydrophobic cavity of subdomain IIA. (c) 2007 Elsevier B.V. All rights reserved.