Pyranopterin dithiolenes xanthine oxidase family

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. 

The occurrence of Mo or W in Nature is, with the exeeption of nitrogenase, always accompanied by a unique pyranopterin dithiolene chelating ligand typically referred to as molybdopterin and this is always coordinated to the metal at the active site. The combination of Mo (or W) with either one or two bidentate molybdopterin ligands in addition to combinations of terminal oxido or sulfido ligands and amino acid side chains leads to an orderly classification of this enzyme family into three sub-groupsthe xanthine oxidase, sulfite oxidase and DMSO reductase families (Scheme 5.1). The eponymous enzyme in each case is historically the first one isolated and studied within its family. 

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