Molybdenum enzyme families

Correlation between PDT dihedral angles and members of the canonical molybdenum enzyme families. Additionally, DFT derived geometries for the Q, T and D PDTs are shown as open circles. ... 

Romao MJ, Huber R (1998) Structure and Function of the Xanthine-Oxidase Family of Molybdenum Enzymes. 90 69-96 Rosenzweig A, see Penneman RA (1973) 13 1-52... 

McEwan AG, IP Ridge, CA McDevitt, P Hugenholtz (2002) The DMSO reductase family of microbial molybdenum enzymes molecular properties and the role in the dissimilatory reduction of toxic elements. 

Huber R, Hof P, Duarte RO, et al. A structure-based catalytic mechanism for the xanthine oxidase family of molybdenum enzymes. Proc Natl Acad Sci USA 1996 93( 17) 8846—8851. 

Figure 17.2 The structure of the pterin cofactor (1) which is common to most molybdenum- and tungsten-containing enzymes and schematic active site structures for members of the xanthine oxidase (2,3), sulfite oxidase (4) and DMSO reductase (5-7) enzyme families. (From Enemark et al., 2004. Copyright (2004) American Chemical Society.)...

Upon purification of the XDH from C. purinolyticum, a separate Se-labeled peak appeared eluting from a DEAE sepharose column. This second peak also appeared to contain a flavin based on UV-visible spectrum. This peak did not use xanthine as a substrate for the reduction of artificial electron acceptors (2,6 dichlor-oindophenol, DCIP), and based on this altered specificity this fraction was further studied. Subsequent purification and analysis showed the enzyme complex consisted of four subunits, and contained molybdenum, iron selenium, and FAD. The most unique property of this enzyme lies in its substrate specificity. Purine, hypoxanthine (6-OH purine), and 2-OH purine were all found to serve as reductants in the presence of DCIP, yet xanthine was not a substrate at any concentration tested. The enzyme was named purine hydroxylase to differentiate it from similar enzymes that use xanthine as a substrate. To date, this is the only enzyme in the molybdenum hydroxylase family (including aldehyde oxidoreductases) that does not hydroxylate the 8-position of the purine ring. This unique substrate specificity, coupled with the studies of Andreesen on purine fermentation pathways, suggests that xanthine is the key intermediate that is broken down in a selenium-dependent purine fermentation pathway. ... 

In the last 5 years, 20 new enzymes have been confirmed to contain either molybdenum or tungsten, and in the last 3 years representive members of both molybdenum and tungsten enzyme families have been crystallographically characterized. 

There are now three different proteins of the XDH/XO family whose structures have been determined by X-ray protein crystallography. The structure of aldehyde oxidoreductase from the bacterium Desulfovibrio gigas was the first X-ray structure determined for an oxo-molybdenum enzyme (17) and has been followed by stmctures of XO/XDH (10) and carbon monoxide dehydrogenase (CODH) (19, 21). Although the three enzymes are placed in the same family, there are structural differences among them at the active site and at the phosphate remote from the Mo center. 

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