DNA facilitating electron transfer reaction of xanthine oxidase

Online electrochemical systems for continuous neurochemical measurements with low-potential mediator-based electrochemical biosensors as selective detectors

This study demonstrates a new strategy to develop online electrochemical systems (OECSs) for continuously monitoring neurochemicals by efficiently integrating in vivo microdialysis with an oxidase-based electrochemical biosensor with low-potential electron mediators to shuttle the electron transfer of the oxidases.

Study of drug metabolism by xanthine oxidase

In this work, we report the studies of drug metabolism by xanthine oxidase (XOD) with electrochemical techniques. Firstly, a pair of stable, well-defined and quasi-reversible oxidation/reduction peaks is obtained with the formal potential at -413.1 mV (vs. SCE) after embedding XOD in salmon sperm DNA membrane on the surface of pyrolytic graphite electrode. Then, a new steady peak can be observed at -730 mV (vs. SCE) upon the addition of 6-mercaptopurine (6-MP) to the electrochemical system, indicating the metabolism of 6-MP by XOD. Furthermore, the chronoamperometric response shows that the current of the catalytic peak located at -730 mV increases with addition of 6-MP in a concentration-dependent manner, and the increase of the chronoamperometric current can be inhibited by an XOD inhibitor, quercetin. Therefore, our results prove that XOD/DNA modified electrode can be efficiently used to study the metabolism of 6-MP, which may provide a convenient approach for in vitro studies on enzyme-catalyzed drug metabolism.

Xanthine dehydrogenase electrocatalysis: autocatalysis and novel activity

The enzyme xanthine dehydrogenase (XDH) from the purple photosynthetic bacterium Rhodobacter capsulatus catalyzes the oxidation of hypoxanthine to xanthine and xanthine to uric acid as part of purine metabolism. The native electron acceptor is NAD(+) but herein we show that uric acid in its 2-electron oxidized form is able to act as an artificial electron acceptor from XDH in an electrochemically driven catalytic system. Hypoxanthine oxidation is also observed with the novel production of uric acid in a series of two consecutive 2-electron oxidation reactions via xanthine. XDH exhibits native activity in terms of its pH optimum and inhibition by allopurinol.

Xanthine oxidase/laponite nanoparticles immobilized on glassy carbon electrode: direct electron transfer and multielectrocatalysis

In this work, colloidal laponite nanoparticles were further expanded into the design of the third-generation biosensor. Direct electrochemistry of the complex molybdoenzyme xanthine oxidase (XnOx) immobilized on glassy carbon electrode (GCE) by laponite nanoparticles was investigated for the first time. XnOx/laponite thin film modified electrode showed only one pair of well defined and reversible cyclic voltammetric peaks attributed to XnOx-FAD cofactor at about -0.370 V vs. SCE (pH 5). The formal potential of XnOx-FAD/FADH(2) couple varied linearly with the increase of pH in the range of 4.0-8.0 with a slope of -54.3 mV pH(-1), which indicated that two-proton transfer was accompanied with two-electron transfer in the electrochemical reaction. More interestingly, the immobilized XnOx retained its biological activity well and displayed an excellent electrocatalytic performance to both the oxidation of xanthine and the reduction of nitrate. The electrocatalytic response showed a linear dependence on the xanthine concentration ranging from 3.9 x 10(-8) to 2.1 x 10(-5)M with a detection limit of 1.0 x 10(-8)M based on S/N=3.