A heterotrimeric membrane-bound fructose dehydrogenase (FDH) complex from Gluconobacter japonicus NBRC3260 catalyzes oxidation of D-fructose into 2-keto-D-fructose and is one of typical enzymes allowing a direct electron transfer (DET)-type bioelectrocatalysis. Subunits I and II have a covalently bound flavin adenine dinucleotide and three heme C moieties, respectively. We have constructed subunit I/III subcomplex (Delta cFDH) lacking of the heme C subunit. Delta cFDH catalyzes the oxidation of D-fructose with several artificial electron acceptors, but loses the DET ability. The formal potentials (E degrees') of the three heme C moieties of FDH have been determined to be -10 +/- 4, 60 +/- 8 and 150 +/- 4 mV (vs. Ag vertical bar AgCl vertical bar sat. KCI) at pH 5.0, while the onset potential of FDH-catalyzed DET-type bioelectrocatalytic wave is - 100 mV. Judging from these results, we conclude that FDH communicates electrochemically with electrodes via the heme C, and discuss the pathway of the electron transfer in the catalytic process. (C) 2013 Elsevier B.V. All rights reserved.