Binding of artemisinin (QHS) to holotransferrin (TF) was investigated by electrochemisty, UV-vis absorption, fluorescence, and circular dichroism (CD) spectra. Electrochemistry results confirm the formation of an electro-active adduct in the interaction between QHS and TF. The binding constant and binding number of the QHS-TF adduct are determined to be 1.64 x 10(5) and 1, respectively. Fluorescence data validate that QHS effectively quenches the intrinsic fluorescence of TF via static quenching, and the hydrogen bonds and van der Waals force play a key role in stabilizing the QHS-TF adduct. Synchronous fluorescence and CD spectra indicate that a drastic conformation change of TF does not take place when QHS is bound to TF. QHS can induce the interchromophoric conformation change of TF, while it does not disturb the iron-bound microenvironment. (C) 2008 Elsevier B.V. All rights reserved.