Po/yhdrm Vol. 8, No. 13/14, pp. 164%1652, 1989 Printed in Great Britain 0277-5387/89 $3.00+.00 0 1989 Maxwell Pqamon Macmillan plc zyxwvuts CHARACTERIZATION OF MOLYBDENUM AND VANADIUM CENTRES IN ENZYMES BY X-RAY ABSORPTION SPECTROSCOPY C. DAVID GARNER,* JUDITH M. ARBER and IAN HARVEY Chemistry Department, Manchester University, Manchester M 13 9PL, U.K. and S. SAMAR HASNAIN The Daresbury Laboratory, Daresbury, Warrington WA4 4AD, U.K. ROBERT R. EADY and BARRY E. SMITH AFRC, IPSR Nitrogen Fixation Laboratory, University of Sussex, Brighton BNl9PQ, U.K. and EIZE de BOER and RON WEVER Laboratory of Biochemistry, University of Amsterdam, 1000 HD Amsterdam, The Netherlands Abstract-Metal K-edge EXAFS studies have provided the only structural evidence so far available for the molybdenum and vanadium centres in enzymes. This paper describes the results of vanadium and iron K-edge EXAFS on the iron-molybdenum and iron-vanadium cofactors of the nitrogenase enzymes for zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML Klebsiella pneumoniae and Azotobacter chro- ococcum, respectively, and the vanadium K-edge EXAFS of the bromoperoxidase from Ascophyllum nodosum. These and other results suggest that molybdenum and vanadium sites in enzymes may be classified in a similar manner: (a) as part of an Fe,MS, (M = MO, V) cubane-like cluster which forms a sub-unit of the cofactor of the nitrogenases; (b) bound to one (or more) 0x0 groups plus sulphur (in the case of molybdenum) or oxygen/nitrogen (in the case of vanadium) ligands to form a catalytic centre for oxygen atom transfer. Both molybdenum and vanadium are clearly recog- nized as being essential for the activity of particular enzymes. ‘-’ The classification of molybdenum-con- taining enzymes is clear, to the extent that the nitro- genases are distinct from the oxomolybdo enzymes, not least in respect of the chemical environment of the molybdenum. Thus, the MoFe-protein of the nitrogenases contains an iron-molybdenum cofactor *Author to whom correspondence should be addressed. (FeMoco), Of approximate COmpOSitiOn9 MOFe&, and oxomolybdo enzymes (such as xanthine oxidase, aldehyde oxidase, sulphite oxidase and nitrate reductase) contain a common molybdenum cofactor (Moco), in which molybdenum is com- plexed by an organic component known as the molybdopterin (1). lo There is much evidence to sup- port the view that the molybdenum-containing co- factor constitutes the catalytic centre of the cor- responding enzyme. Vanadium is now clearly recognized as an essen- 1649