Acetylene hydratase

Acetylene hydratase from the anaerobe Pelobacter acetylenicus is a tungsten-iron-sulfur enzyme that resembles molybdopterin with W replacing Mo (Meckenstock et al. 1999), and catalyzes the addition of the elements of water to acetylene (Figure 3.30a). 

Meckenstock RU, R Krieger, S Ensign, PMH Kroneck, B Schink (1999) Acetylene hydratase of Pelobacter acetylenicus. Molecular and spectroscopic properties of the tungsten iron-sulfur enzyme. Eur J Biochem 264 176-182. 

The acetylene hydratase of Pelobacter acetylenicus (Rosner and Schink 1995). 

Rosner BM, B Schink (1995) Purification and characterization of acetylene hydratase of Pelobacter acetyle-nicus, a tungsten iron-sulfur protein. J Bacterial 177 5767-5772. 

Again, these appear to resemble the corresponding Mo-dependent enzymes. The unique acetylene hydratase from the acetylene-utilizing Pelobacter acetylenicus catalyzes the hydration of acetylene to acetaldehyde.687... 

Acetylene hydratase Pyrogallol transhydroxylase Bacterial Bacterial a LW( )s,h (MPTpG)Mo( )h Unknown Unknown 2 Fe2S2 6 Fe2S2, FAD 74 77,80,81... 

The divalent ions Mg2+, Ca2+, and Zn2+ have long been known to serve as Lewis acids in important biological processes [223,224], As Lewis acids, these metals either activate substrate toward hydrolysis or activate a nucleophile such as water or serine. The high-valent tungsten site in acetylene hydratase may play one (or both) of these roles. 

Acetylene hydratase [74] is unique among the molybdenum and tungsten enzymes. This enzyme catalyzes the hydration of an unsaturated organic substrate, acetylene, a reaction that is neither an oxidation nor a reduction. Although tungsten may assume different oxidation states, the non-redox nature of the sub-... 

Mechanisms of action for the metal centers in acetylene hydratase, polysulfide reductase, and formate dehydrogenase have been briefly described in Sections VI.A and VLB. The discussion, in each case, was relatively straightforward insofar as the natures of these reactions lend themselves to simple mechanistic proposals. The mechanism by which the metal centers function in most of the other Mo and W enzymes is not as obvious. We elect to discuss mechanistic roles for the molybdenum centers in xanthine oxidase, sulfite oxidase, and dmso reductase. These enzymes are representative members of each large class of molybdenum enzymes, and the large body of literature on each enzyme makes detailed discussion possible. 

Hydration and/or dehydration reactions are frequently catalyzed by metallopro-teins. Examples are proteins containing nickel (urease), zinc (e.g., peptidases), molybdenum (the hydratase partial reaction of formate oxidoreductase), tungsten (acetylene hydratase). An obvious difference between Ni, Zn, on the one hand, and Fe, Mo, W, on the other, is that the first are directly coordinated to the protein whereas the latter are also part of a cofactor. With reference to the Fe/S cluster in aconitase it has been suggested that cofactor coordination may provide an added flexibility to the active site, in particular to the substrate binding domain [15],... 

Rosner, B. M., Rainey, F. A., Kroppenstedt, R. M., and Schink, B., 1997, Acetylene degradation by new isolates of aerobic bacteria and comparison of acetylene hydratase enzymes, FEMS Microbiol Lett. 148 175nl80. 

Formate dehydrogenase Acetylene hydratase Aldehyde oxidoreductase... 

In contrast to the Mo oxo-transfer enzymes, the majority of the W enzymes only catalyse aldehyde oxidation or its equivalent, i.e. oxygen atom transfer to a carbon, with acetylene hydratase being a notable exception. However, iso-enzymes, in which W is substituted for Mo - the metal normally incorporated by biology in these systems - have been identified and these are extending the range of W oxo-transfer enzymes. Studies of the relative behaviours of these two metals at the same catalytic site are now beginning to reveal interesting differences in their kinetics and thermodynamics (see Section 3.2). 

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