A promoted electron transfer of an antitumor drug, mitoxantrone (MTX), intercalating into DNA duplex was successfully obtained upon addition of cytochromes c (cyt. c) in NaAc-HAc buffer solution (pH 4.5). The experimental results suggested that co-existence of MTX and cyt. c in the DNA helix is an important factor for accelerated electron transfer of MTX, where the promoter, cyt. c, operated smoothly through the DNA bridge. The UV/Vis spectroscopic experiments further confirmed the interaction process. Furthermore, a possible mechanism of such reaction was also discussed in this paper. (c) 2005 Elsevier Inc. All rights reserved.