Human xanthine oxidoreductase: in search of a function.
نویسنده
چکیده
The molybdoenzyme, xanthine oxidoreductase (XOR), has been much studied, largely because of its ready availability on a large scale from cows' milk [ l ] . It catalyses the oxidation of a wide range of substrates, most notably hypoxanthine and xanthine, generating xanthine and uric acid respectively, in the process of purine catabolism. The enzyme is a homodimer of 150 kDa subunits and exists in two interconvertible forms, xanthine dehydrogenase (XDH; EC 1.1.1.204) and xanthine oxidase (XO; EC 1.1.3.22). XDH preferentially reduces NAD', whereas XO does not reduce NAD', preferring molecular oxygen. Reduction of oxygen by either form of the enzyme yields 0;' and H202, and it is the capacity to generate such reactive oxygen species (ROS) that has led to a great deal of interest in XOR as a pathogenic factor in many instances of ischaemia-reperfusion injury [2]. More recently, an increasing body of evidence suggests a role for ROS in normal signal transduction [3-51. The commonly cited mechanism involving XOR in ischaemia-reperfusion injury [6,7] can be summarized as follows. During ischaemia the cell's energy charge falls and transmembrane ion gradients are dissipated, leading to elevated cytosolic concentrations of CaZ+. This in turn activates a protease that irreversibly converts XDH, predominant in vi'uo, into XO. Concurrently, depletion of cellular ATP leads to AMP, which is catabolized successively to adenosine, inosine
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ورودعنوان ژورنال:
- Biochemical Society transactions
دوره 25 3 شماره
صفحات -
تاریخ انتشار 1997