Mononuclear tungsten and molybdenum metalloenzymes play significant roles in the global carbon, nitrogen, and sulfur cycles, and are found in countless organisms. Tungsten is the only known 3rd row transition metal currently found in metalloenzymes and 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/energy acquisition. The crystal structure of AH suggests that the oxygen derived ligand is either a hydroxo or aqua ligand. Previously we have utilized the known AH model complex, [Et4N]2[WIV(O)(mnt)2], to determine the kinetics of coordination of bulky acetylene derivatives such as diethyl or dimethyl acetylenedicarboxylate (DEAD or DMAD, respectively). While these studies were able to elucidate the associative mechanism of this model complex, it is hypothesized that formation of a hydroxylated complex should substantially increase the rate of coordination of the acetylenic compounds, not only due to its increased likeness relative to the native enzyme’s active site, but because of the reduced reorganization energy it would afford upon coordination with an acetylene derivative. Attempts to synthesize and characterize a stable complex with the formula [WIV(OR)(mnt)2]– or [WIV(solv)2(mnt)2]– are currently underway in order to test its coordination kinetics in relation to [WIV(O)(mnt)2]2- as well as to further our understanding of the possible identity of the oxygen-derived ligand of AH, and how the identity of this ligand affects the enzyme’s kinetics.

Increasing the coordination kinetics of the Acetylene Hydratase (AH) model complex via pseudo-hydroxylation

253rd National Meeting (2017)

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