Xanthine oxidase: introductory remarks.

At the 661st Meeting of the Biochemical Society, held at Bath, the Host Colloquium, a joint meeting with the Society for Free Radical Research, took place on 10th and 11th April 1997. Its title was ‘Xanthine oxidase: enzymology and pathophysiology’. The two aspects of xanthine oxidase research specified in the Colloquium title have developed remarkably separately, and, for a number of reasons, it now seemed timely to bring together two groups of workers with quite different approaches to study of the same enzyme. Xanthine oxidase is a complex enzyme, containing molybdenum, FAD and ironlsulphur redox centres, that has been known for at least 95 years and studied as the essentially pure enzyme for nearly 60 years. Its ready availability on a large scale from cows’ milk has allowed the enzyme to become a model for structural and mechanistic analysis of molybdoenzymes in general, by EPR, stopped flow, X-ray absorption fine structure and other physicochemical techniques. The last few years have seen a sharp increase in structural information, with determination of sequences of xanthine dehydrogenasel oxidase from several sources, elucidation of the structure of the molybdenum cofactor and, suddenly at a late stage in the development of the field, publication of the three-dimensional structure of one very closely related and two additional molybdoenzymes. These recent advances have greatly facilitated mechanistic studies of molyb-