Oxotransferase

Others oxotransferases) (2 pyranopterins bonded to Mo) (8-10 members) Nitrate reduction dissimilatory terminal respiratory oxidase Pyridoxal oxidase Xanthine dehydrogenases Pyrogallol transhydrolase Nitrate to nitrite... 

Tungsten catalysts are also known, and are of considerable interest because they are mimics for tungsten-based oxotransferase enzymes found in thermochemical bacteria. Studies on such compounds have been reported (16,17). 

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

The activation of oxygen in oxygen transfer reactions is usually mediated by a suitable transition metal catalyst which has to be sufficiently stable under the reaction conditions needed. But also non-metal catalysts for homogeneous oxidations have recently been of broad interest and several of them have been compiled in a recent review.2 Other examples for well known alkene oxidation reactions are the ozonolysis, hydroboration reactions or all biological processes, where oxygen is activated and transferred to the substrate. Examples for these reactions might be cytochrome P450 or other oxotransferases. Of these reactions, this contribution will focus on transition-metal mediated epoxidation and dihydroxylation. 

FIGURE 7. The catalytic properties of dioxo Mo(VI) compounds relevant to the eukaryotic oxotransferases. 

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. 

The enzymes are subdivided into three families based on structural and sequence comparisons (Figure 1, Table 1). Oxotransferases isolated from prokaryotes (see Prokaryote) belong to the DMSO reductase family. These enzymes include DMSO reductase, biotin X-oxide reductase, trimethylamine A-oxide reductase, dissimilatory nitrate reductase, formate... 

Two overall mechanisms have been considered for snch reactions one (Scheme 3) occurs via an electrophilically activated oxo-donor (XO) toward the oxo-acceptor (Y), npon coordination to a Lewis acid ReO center and the other one (Scheme 4) involves a metal-centered oxygen transfer via a Re 0 / Re 02 couple that parallels that of Mo oxotransferases (via the isoelectronic Mo /Mo couple). 

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. 

Understanding Oxotransferase Reactivity in a Model System Using Singular Value Decomposition Analysis... 

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. 

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