Studies of Molybdenum and Tungsten Enzymes

There are several recent reviews of the molybdenum and tungsten enzymes [4-6,23,26-36], In this chapter, we first define the metallocofactors and offer a compilation of the enzymes and their diverse activities. We then focus on the active-site structures, highlighting the confluence of crystallographic and spectroscopic studies. This is followed by a discussion of pertainent spectroscopic, structural, reactivity, and theoretical model studies. We then turn our attention to the mechanisms of catalytic activity of the molybdenum and tungsten enzymes. 

From recent x-ray crystallographic studies of both molybdenum and tungsten enzymes, MPT is now known to be a C(6)-substituted 5,6-dihydropterin that is covalently alkoxylated at the C(7) position by the alcohol of the 1,2-enedithio-late side chain (Eq. 1) [39],... 

Chemical systems of relevance to the molybdenum and tungsten enzymes include synthetic pterins, a-phosphorylated ketones (as precursor models), and a variety of molybdenum and tungsten oxido, sulfido, and 1,2-enedithiolate complexes. These compounds have been used to (1) confirm the identity of MPT derivatives (2) define steps in MPT biosynthesis (3) calibrate spectroscopic observations (4) give precise geometries and reactivities that can be used as input for theoretical studies and (5) provide options for mechanistic consideration. 

The vast majority of studies, either on molybdenum and tungsten enzymes or on small molecule models for them, have focused on the metal and probed its... 

Thanks to several protein crystallographic studies and a wealth of spectroscopic information, we now have a good basis for understanding the structure-function relationships of the molybdenum and tungsten enzymes. In each... 

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