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This paper describes a batch-type coulometric D-fructose biosensor based on direct electron transfer reaction of D-fructose dehydrogenase (FDH) adsorbed on a porous carbon electrode surface. The adsorbed-FDH electrodes catalyzed the electrochemieal two-electron oxidation of D-fructose to 5-keto-D-fructose without a mediator. Nanostructured carbon particle-modified electrodes were used for the coulometric D-fructose biosensor to enhance the catalytic current density. The electric charge for the D-fructose oxidation gained by the biocoulometric measurement was in good agreement with the theoretical value corresponding to D-fructose amount in the range from 1 to 100 mM with a sample volume of I [micro]L. This method is also applicable to the determination of several oligo/ palysaccharides containing the D-fructose unit, in combination with specific hydrolases to yield D-fructose. An example was demonstrated by sucrose determination in which the electrode modified with FDH and invertase was used as a working electrode. To address the problem of electroactive interferences such as ascorbate, the electric charge at the FDH-free electrode was subtracted from the total charge obtained at the FDH-adsorbed electrode. The D-fructose concentrations in several beverages were successfully determined with this method. 10.1021/ac901771t

Tungsten-containing formate dehydrogenase from Methylorubrum extroquens AM1 (FoDH1)—a promising biocatalyst for the interconversion of carbon dioxide/formate and nicotine adenine dinucleotide (NAD+)/NADH redox couples—was investigated using structural biology and bioelectrochemistry. FoDH1 is reported to be an enzyme that can realize "direct electron transfer (DET)-type bioelectrocatalysis." However, its 3-D structure, electrode-active sites, and electron transfer (ET) pathways remain unclear. The ET pathways were investigated using structural information, electrostatic interactions between the electrode and the enzyme, and the differences in the substrates. Two electrode-active sites and multiple ET pathways in FoDH1 were discovered. [ABSTRACT FROM AUTHOR]

The catalytic reaction of glucose oxidase (GOx) mediated by 3-(10-phenothiazyl)propionic acid (PT-PA) and phenothiazine-labeled poly(ethylene oxide) (PT-PEO1000) that are covalently bonded to Au(111) electrodes has been investigated. The PT-PA and PT-PEO1000 are reacted with 2-aminoethanethiol (AET), followed by the formation of a self-assembled monolayer (SAM) onto the Au surface. The PT group immobilized on the SAM of AET acts as an effective mediator for the electron transfer (ET) between the electrode and the FAD center of freely diffusing GOx in solution. The ET rate constant estimated from the catalytic current using a newly derived equation is larger by 1 order of magnitude for the PT-PA-modified system (1.1 x [l0.sup.5] d[m.sup.3] [mo1.sup.-1] [s.sup.-l]) than for the PT-PEO1000 system (1.4 x [10.sup.4] d[m.sup.3] [mol.sup.-1] [s.sup.-l]). The order of the magnitude of the ET rate constant clearly contrasts with the GOx hybrid systems that we previously investigated (Anal. Chem. 2003, 75, 910-917), in which the presence of the PEO spacer enhances the ET reaction rate. The reduction in the apparent PT concentration at the electrode interface due to the high mobility of the PEO chain, leading to low efficiency in the formation of an enzyme-mediator complex, is a possible reason for the lower mediation ability of PT-PEO1000 than that of PT-PA for the ET between the FAD group and P[T.sup.+] immobilized on the electrode. Inhibition of the penetration of GOx molecules into the monolayer and of the accessibility of some part of PT groups to GOx molecules could also be reasons for the lower mediation ability of PT-PE01000 thickly modified on the electrode.

Research has been conducted on Paracoccus denitrificans quinohemoprotein amine dehydrogenase. The study of quinohemoprotein amine dehydrogenase's hemes c carried out via the use of mediator-assisted continuous-flow column electrolytic spectroelectrochemistry is presented.

Mediated biosensors consisting of an oxidase and peroxidase (POx) have attracted increasing attention because of their wide applicability. However, since most of oxidases utilize artificial electron acceptors in place of dioxygen, the competition between [O.sub.2] and the electron acceptor in the mediated sensors is anticipated. This has been evidenced with a glucose oxidase (GOx)- and POx-coentrapped and ferrocene-embedded carbon paste electrode, which exhibits peak-shaped current-time curves at increased concentrations of glucose and also gives a peak-shaped calibration curve. Digital simulation has been applied to clarify the cause of such unusual responses, by taking into account the ping-pong enzyme kinetics on two- and three-substrate models for POx and GOx, respectively. The simulation has well reproduced such unusual responses and has clearly revealed that the depletion of [O.sub.2] in the enzyme layer is the most important factor responsible for such unusual responses. To overcome such a drawback of oxidase/POx bienzyme sensors, it is expected to be essential to decrease the rate of the oxidase reaction. In contrast, increase in the POx activity is useful to improve the sensitivity. According to the simulation-based expectation, the GOx and POx concentrations in the bienzyme sensor are adjusted to exhibit normal behavior with high sensitivity.