Molybdenum enzymes structure

Molybdenum enzymes a survey of structural information from EXAFS and EPR spectroscopy. S. P. Cramer, Adv. Inorg. Bioinorg. Mech., 1983, 2, 260 (137). 

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... 

Kisker, C., Schindelin, H. and Rees, D.C. (1997). Molybdenum cofactor - containing enzymes structure and mechanisms. Annu. Rev. of Biochem., 66, 233-267... 

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. 

The evidence for a pterin-substituted 1,2-enedithiolate was first reported by Raja-gopalan, Johnson, and coworkers, who isolated pterins from the oxidative decomposition of molybdenum-bound MPT, Figure 4 [7,49,55,56], In complementary work, Taylor and coworkers confirmed the structure of several of the pterin decomposition products by direct synthesis (see Section V. A) [30,57-59], Urothi-one, first isolated in 1940 from human urine [60], was shown to be a metabolic degradation product of MPT [37], Other isolated pterin-containing decomposition and/or derivatized products from molybdenum enzymes include Form A, Form B (a urothione-like product), and camMPT (Figure 4) [7], Two other pterins, Form Z and the MPT precursor, can be obtained from molybdenum deprived organisms, N. crassa Nit-1, and oxidase-deficient children, neither of which pro-... 

Of all of the molybdenum enzymes, mammalian xanthine oxidase/dehydrogenase has been the most studied (Figure 15). These studies, along with those of other members of this relatively large class of hydroxylases (Table la-c), suggest that all molybdenum enzymes that catalyze hydroxylation of C—H bonds contain a common structural motif. This motif is unique in high-valent molybdenum chem-... 

Mechanistic speculations about the molybdoenzymes must be considered to be in their infancy with the possible exception of those for xanthine oxidase. Although the detailed structural nature of the molybdenum site is unknown, there is sufficient information from biochemical and coordination chemistry studies to allow informed arguments to be drawn. Here we first discuss evidence for the nuclearity of the molybdenum site and then discuss both oxo-transfer and proton-electron transfer mechanisms for molybdenum enzymes. A final discussion considers the unique aspects of nitrogenase and the possible reasons for the use of molybdenum in enzymes. 

The most detailed spectroscopic and electronic structure studies of metallo-mono(dithiolenes) have focused on the nature of ligand-to-ligand charge transfer (LLCT) excitations in [M(diimine)(dithiolene)] complexes (112, 250-257, 262, 264, 295-301) and in monooxo molybdenum dithiolenes (19, 20, 22, 23) as models for pyranopterin molybdenum enzymes such as sulfite oxidase (SO). Since metallo-mono(dithiolenes) generally possess little or no symmetry, detailed spectrosopic and electronic structure studies of this class of metallo-dithiolenes have only recently begun to appear. The analysis of the spectroscopic data has been aided by the fact that the dithiolene-to-metal charge... 

The dithiolene structural unit that is common and required by all Mo and W enzymes was only recently identified definitively. After several decades of active research on molybdenum enzymes, conclusive structural evidence for the dithiolene piece was available as recently as 1995 (42). 

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. 

---