Mononuclear tungsten and molybdenum metalloenzymes play significant roles in the global carbon, nitrogen, and sulfur cycles, and are found in nearly all organisms. Tungsten is the only known 3rd row transition metal currently found in metalloenzymes. All tungstoenzymes known to date are found in anaerobic, thermophilic bacteria and hyperthermophilic archaea. Acetylene hydratase (AH) is a tungsten-containing enzyme that catalyzes the nonredox hydration of acetylene (C2H2) to acetaldehyde (CH3CHO). AH is unique in several aspects: (1) it is the only known nonredox Mo/W enzyme, (2) it is the only known enzyme to use C2H2 as its native substrate, and (3) these organisms use C2H2 as their sole carbon and energy source, for which AH catalyzes the first step in carbon and energy acquisition. Chemical routes to the hydration of acetylene are known, but the mechanism of AH remains elusive. To date three reaction mechanisms have been proposed computationally, two of which invoke the formation of a WIV(η2-C2H2) complex. The purpose of this research was to gain a better understanding of the reaction mechanism of AH by experimentally determining if a viable WIV(η2-C2H2) complex forms. A known tungsten model complex was utilized that mimics the active site of AH, and this complex was then reacted with different acetylene derivatives (RC2R’) in order to determine whether coordination between the acetylene derivative and the tungsten center of the model complex occurred. The identity of the oxygen-donor ligand and its role in substrate coordination was also explored.

Toward understanding the reaction mechanism of the tungstoenzyme, acetylene hydratase

249th National Meeting (2015)

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