Molybdenum oxotransferase

Barber, M.J. Neame, P.J. (1990). A conserved cysteine in molybdenum oxotransferases. Journal of Biological Chemistry 265, 20912-15. 

Schultz, B. E., Gheller, S. F., Muetterties, M. C., Scott, M. J., and Helm, R. H., 1993, Molybdenum-mediated oxygen atom h ansfer an improved analogue reaction system of the molybdenum oxotransferases, J. Am. Chem. Soc. 115 2714fi2722. 

For several years, we have been investigating the molecular events of oxygen atom transfer (OAT) reactions involving oxo-molybdenum complexes as models for molybdenum oxotransferases (7-7). The overdl reaction is shown in eq 1. 

Figure 20.13 (a) Catalytic cycle of molybdenum oxotransferase mimic 41, (b) cationic soluble sterically protected imido molyb-... 

First steps toward highly elaborate functional artificial metalloenzymes including active site and microenvironment and comprising fundamental aspects of structural, spectroscopic, and, most importantly, functional similarities toward natural systems have been highlighted in this review. Hydrolysis reactions (phos-phor(di)esterases), C-C and C-X bond formations (ACS), X-O bond formation (molybdenum oxotransferase) and multielectron redox reactions (H2ase, N2ase,... 

The molybdenum-containing oxidoreductases that catalyze Eq. (1) have been variously termed molybdenum hydroxylases (6), oxotransferases (7), and oxo-type molybdenum enzymes (8). Molybdenum hydroxylase aptly describes the conversion of xanthine to uric acid, but the name seems less appropriate for the reactions catalyzed by sulfite oxidase and nitrate reductase oxotransferase implies that the function of these enzymes is to transfer oxo groups, even though relatively little is known about their actual mechanism of action and the name oxo-type molybdenum enzyme recognizes both the apparent oxo transfer chemistry of Eq. (1) and the fact that the molybdenum atom in each of these enzymes contains at least one terminal oxo group. In this chapter, we shall refer to these enzymes as pterin-containing molybdenum enzymes because a 6-substituted pterin appears to be a common chemical feature of all of the enzymes. 

Catalytic and single-turnover experiments with the R. sphaeroides DMSO reductase, 0-labeled DMSO and l,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane as an oxygen atom acceptor have been used to demonstrate that the enzyme is an oxotransferase. Complementary resonance Raman studies have been interpreted on the basis of a direct mechanism for OAT, with the active site cycling between mono-oxo-Mo(VI) and des-oxo-Mo(IV) forms via a DMSO-bound Mo(IV) intermediate. Both MPT dithiolene groups stay firmly attached to the molybdenum throughout the catalytic cycle. However, EPR and UV/visible spectroscopic evidence has been interpreted on the basis of the species formed upon the addition of DMS to oxidized... 

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