Electrochemistry of the flavodehydrogenase domain of flavocytochrome b2 engineered for l-mandelate dehydrogenase activity

The direct electrochemistry of the flavodehydrogenase domain of flavocytochrome b2 engineered for l-mandelate dehydrogenase activity (FDH) has been investigated at an edge-plane pyrolytic graphite (EPG) electrode using poly-l-lysine as a promoter. Two redox couples (−0.481 and −0.605 V vs. SCE in Tris buffer solution at pH 7.5, scan rate 20 mV s−1) were obtained on the cyclic voltammogram which correspond to the separated two peaks in the one-electron reduction-reoxidation steps of enzyme bounded flavin mononucleotide (FMN). The electrochemical transformation of the substrate l-mandelic acid (LMA), catalysed by the FMN-domain of l-mandelate dehydrogenase (LMDH) is inhibited at bare or promoter-modified EPG, but both ferrocenemonocarboxylic acid (FMCA) and cytochrome c function as mediators.