TY  - JOUR
A1  - Kalimuthu, Palraj
A1  - Leimkühler, Silke
A1  - Bernhardt, Paul V.
T1  - Catalytic electrochemistry of xanthine dehydrogenase
JF  - The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces & biophysical chemistry
N2  - We report the mediated electrocatalytic voltammetry of the molybdoenzyme xanthine dehydrogenase (XDH) from Rhodobacter capsulatus at a thiol-modified Au electrode. The 2-electron acceptor N-methylphenazinium methanesulfonate (phenazine methosulfate, PMS) is an effective artificial electron transfer partner for XDH instead of its native electron acceptor NAD(+). XDH catalyzes the oxidative hydroxylation of hypoxanthine to xanthine and xanthine to uric acid. Cyclic voltammetry was used to generate the active (oxidized) form of the mediator. Simulation of the catalytic voltammetry across a broad range of substrate and PMS concentrations at different sweep rates was achieved with the program DigiSim to yield a set of consistent rate and equilibrium constants that describe the catalytic system. This provides the first example of the mediated electrochemistry of a xanthine dehydrogenase (or oxidase) that is uncomplicated by interference from product oxidation. A remarkable two-step, sequential oxidation of hypoxanthine to uric acid via xanthine by XDH is observed.
Y1  - 2012
U6  - https://doi.org/10.1021/jp307374z
SN  - 1520-6106
VL  - 116
IS  - 38
SP  - 11600
EP  - 11607
PB  - American Chemical Society
CY  - Washington
ER  - 
TY  - JOUR
A1  - Kalimuthu, Palraj
A1  - Leimkühler, Silke
A1  - Bernhardt, Paul V.
T1  - Low-potential amperometric enzyme biosensor for xanthine and hypoxanthine
JF  - Analytical chemistry
N2  - The bacterial xanthine dehydrogenase (XDH) from Rhodobacter capsulatus was immobilized on an edge-plane pyrolytic graphite (EPG) electrode to construct a hypoxanthine/xanthine biosensor that functions at physiological pH. Phenazine methosulfate (PMS) was used as a mediator which acts as an artificial electron-transfer partner for XDH. The enzyme catalyzes the oxidation of hypoxanthine to xanthine and also xanthine to uric acid by an oxidative hydroxylation mechanism. The present electrochemical biosensor was optimized in terms of applied potential and pH. The electrocatalytic oxidation response showed a linear dependence on the xanthine concentration ranging from 1.0 X 10(-5) to 1.8 X 10(-3) M with a correlation coefficient of 0.994. The modified electrode shows a very low detection limit for xanthine of 0.25 nM (signal-to-noise ratio = 3) using controlled potential amperometry.
Y1  - 2012
U6  - https://doi.org/10.1021/ac3025027
SN  - 0003-2700
VL  - 84
IS  - 23
SP  - 10359
EP  - 10365
PB  - American Chemical Society
CY  - Washington
ER  -