2 research outputs found
Mediatorless Direct Electron Transfer between Flavin Adenine Dinucleotide-Dependent Glucose Dehydrogenase and Single-Walled Carbon Nanotubes
The
flavoenzymes flavin adenine dinucleotide-dependent glucose
dehydrogenase (FAD-GDH) and oxidase (FAD-GOx) do not undergo direct
electron transfer (DET) at conventional electrodes, because the flavin
adenine dinucleotide (FAD) cofactor is buried deeply (∼1.4
nm) below the protein surface. We present a mediator-less DET between
oxygen-insensitive FAD-GDH and single-walled carbon nanotubes (SWCNTs).
A glucose-concentration-dependent current (GCDC) is observed at the
electrode with the combination of glycosylated FAD-GDH and debundled
SWCNTs; the GCDC, because of an increase in the polarized potential
during potential sweep voltammetry, increases steeply (+0.1 V of onset,
1.2 mA cm<sup>–2</sup> at +0.6 V 48 mM glucose) without the
appearance of the FAD redox peak at −0.45 V. In the control
experiment, the GCDC is not observed at the counterpart with either
bundled SWCNTs or debundled multiwalled carbon nanotubes (MWCNTs).
In the control experiment, the GCDC is observed at an analogous electrode
based on oxygen-sensitive FAD-GOx with all CNT types (bundled SWCNTs,
debundled SWCNTs, and debundled MWCNTs) in the presence of oxygen
because oxygen acts as a natural and mobile mediator. Therefore, observation
of the GCDC at the electrode with oxygen-insensitive FAD-GDH and debundled
SWCNTs provides evidence of mediator-less DET, even though oxygen
is present. Details of the DET are discussed with respect to the recently
reported crystallographic model of FAD-GDH. The three-dimensional
globular FAD-GDH molecule is 4.5 nm × 5.6 nm × 7.8 nm, which
is larger than the 1.2 nm diameter of an individual SWCNT and smaller
than the 10 nm diameter of an individual MWCNT and the 1 μm
size of a SWCNT bundle. Only individual SWCNTs can be plugged into
the groove of FAD-GDH, which is close to and within 1.0 nm of FAD,
while maintaining their catalytic activity. Images obtained using
transmission electron and atomic force microscopies support the stated
configuration of FAD-GDH molecules and debundled SWCNTs. We demonstrate
that DET can be explained by quantum tunneling theory. Electrochemical
experiments with various FAD-GDHs suggest that (i) DET with debundling
SWCNT can be applied to any type of FAD-GDH, (ii) the electrode with
various types of FAD-GDH implements superior functions (compared to
an analogous electrode with FAD-GOx and nicotineamide adenine dinucleotide-GDH),
and (iii) glycan chains present on FAD-GDH prevent denaturation when
the SWCNT is close to FAD
Thermophilic <i>Talaromyces emersonii</i> Flavin Adenine Dinucleotide-Dependent Glucose Dehydrogenase Bioanode for Biosensor and Biofuel Cell Applications
Flavin adenine dinucleotide (FAD)-dependent
glucose dehydrogenase
(GDH) was identified and cloned from thermophilic filamentous fungi Talaromyces emersonii using the homology cloning
method. A direct electron transfer bioanode composed of T. emersonii FAD-GDH and a single-walled carbon nanotube
was produced. Enzymes from thermophilic microorganisms generally have
low activity at ambient temperature; however, the T.
emersonii FAD-GDH bioanode exhibits a large anodic
current due to the enzymatic reaction (1 mA cm<sup>–2</sup>) at ambient temperature. Furthermore, the T. emersonii FAD-GDH bioanode worked at 70 °C for 12 h. This is the first
report of a bioanode with a glucose-catalyzing enzyme from a thermophilic
microorganism that has potential for biosensor and biofuel cell applications.
In addition, we demonstrate how the glycoforms of T.
emersonii FAD-GDHs expressed by various hosts influence
the electrochemical properties of the bioanode