Direct electrochemistry of histamine dehydrogenase from Nocardioides simplex

Histamine dehydrogenase from Nocardioides simplex (HmDH) belongs to the family of soluble iron–sulfur flavoproteins having one [4Fe–4S] cluster and one 6-S-cysteinyl flavin mononucleotide per monomer. Direct electrochemistry of HmDH was studied using several carbon particle-modified glassy carbon electrodes (GCEs) and indium tin oxide (ITO) electrodes. HmDH gave a clear catalytic wave of the histamine oxidation without any mediator at a GCE modified with Ketjen Black (KB) with an average particle diameter of 39.5 nm, although redox signal of the cofactors itself was not clearly recognized. Experimental data supported the irreversible adsorption of HmDH on the KB particles and the importance of the size of the carbon particle as well as the surface area as factors determining the current density of the direct electron transfer (DET)-type bioelectrocatalysis. On the other hand, HmDH was adsorbed on ITO electrodes as a monolayer, as evidenced by quartz crystal microbalance measurement, and showed a clear redox wave ascribed to the [4Fe–4S] cluster. However, some mediators were required to observe catalytic wave of histamine oxidation at ITO electrodes, indicating that the interaction between the two redox cofactors seems to be disrupted in the monomer HmDH adsorbed on the planar and hydrophilic surfaces of ITO electrodes. Surface properties of electrodes favorable for DET-type bioelectrocatalysis of HmDH are discussed.