Electron paramagnetic resonance xanthine oxidase

The possibility that there might be long-range electron transfer between redox-active centers in enzymes was first suspected by biochemists working on the mechanism of action of metalloenzymes such as xanthine oxidase which contain more than one metal-based redox center. In these enzymes electron transfer frequently proceeds rapidly but early spectroscopic measurements, notably those by electron paramagnetic resonance, failed to provide any indication that these centers were close to one another. 

Bray, R. C., and VAnngArd, T., 1969, eRapidly appearing molybdenum electron paramagnetic resonance signals from reduced xanthine oxidase, Biochem. J. 114 725n734. 

As yet, no X-ray crystal structures are available for any of the molybdenum enzymes in Table I. Therefore, present descriptions of the coordination environment of the molybdenum centers of the enzymes rest primarily upon comparisons of the spectra of the enzymes with the spectra of well-characterized molybdenum complexes. The two most powerful techniques for directly probing the molybdenum centers of enzymes are electron paramagnetic resonance (EPR) spectroscopy and X-ray absorption spectroscopy (XAS), especially the extended X-ray absorption fine structure (EXAFS) from experiments at the Mo K-absorption edge. Brief summaries of techniques are presented in this section, followed by specific results for sulfite oxidase (Section III.B), xanthine oxidase (Section III.C), and model compounds (Section IV). 

Electron paramagnetic resonance spectroscopy showed that xanthine/xanthine oxidase in cultured rat cardiomyocytes produced superoxide and hydroxyl radicals during 10 min (Durot et al. 2000). The xanthine/xanthine oxidase system altered sharply and irreversibly the spontaneous electrical and mechanical activities of the cardiomyocytes. However, the gas chromatographic analysis showed that these drastic functional damages were associated with comparatively moderate degradation of membrane polyunsaturated fatty acids. Moreover... 

---