Governing Generation and Interconversion of the Signals

Introduction and Nomenclature Functional and Desutfo Xanthine Oxidase 

Oxidation-Reduction Potentials Associated with Molybdenum in Enzymes 

It was found in early studies on xanthine oxidase (Bray et al, 1961) that, under certain conditions at least, Mo(V) signals appeared on addition of small amounts of reductant to the enzyme, to disappear again in the presence of excess reductant. This phenomenon was attributed, provisionally, to equilibria of the type 

However, achieving a full understanding of the system came slowly, largely because of complications caused by slow equilibration of the desulfo enzyme with the functional enzyme system. Thus, it was not until much later that the relative (Olson et al, 1974) or the absolute (Bray et al, 1975 Cammack et al, 1976) redox potentials for equation (2) could be estimated for functional and for desulfo xanthine oxidase. 

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