Xanthine oxidase, activation volume

In the xanthine/xanthine oxidase-cytochrome c method originally developed by McCord and Fridovich (M19), a typical assay mixture consists of oxidized1 cytochrome c, xanthine, sufficient xanthine oxidase, and phosphate buffer at pH 7.8 containing EDTA in a total volume of 3 ml. The rate of reaction is followed at 550 nm. One unit of SOD activity is defined as the amount that causes 50% inhibition of the rate of reduction of cytochrome c. 

The initial contribution to this volume provides a detailed overview of how spectroscopy and computations have been used in concert to probe the canonical members of each pyranopterin Mo enzyme family, as well as the pyranopterin dithiolene ligand itself. The discussion focuses on how a combination of enzyme geometric structure, spectroscopy and biochemical data have been used to arrive at an understanding of electronic structure contributions to reactivity in all of the major pyranopterin Mo enzyme families. A unique aspect of this discussion is that spectroscopic studies on relevant small molecule model compounds have been melded with analogous studies on the enzyme systems to arrive at a sophisticated description of active site electronic structure. As the field moves forward, it will become increasingly important to understand the structure, function and reaction mechanisms for the numerous non-canonical [ie. beyond sulfite oxidase, xanthine oxidase, DMSO reductase) pyranopterin Mo enzymes. 

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