(617e) Syngas Fermentation: Reaction Kinetics and Pressure Dependencies of the Clostridial P11 Hydrogenase Enzyme

Ethanol usage as a transportation fuel is rapidly increasing in the United States. Production of ethanol from cellulose feedstocks via gasification followed by syngas fermentation offers an approach that mitigates many of the adverse effects associated with production of ethanol from corn. In the syngas fermentation process, the hydrogenase enzyme of the fermentation bacterium supplies electrons to the metabolic pathway, facilitating ethanol production.

Though it is possible for the metabolic pathway to obtain electrons from CO oxidation during syngas fermentation, it is preferred to obtain electrons from H₂ as this leaves the CO available for incorporation into the desired organic chemicals. Processes that depend on CO oxidation to supply electrons greatly reduce their carbon-to-product yield. Hence, understanding the kinetics of H₂ oxidation via hydrogenase may facilitate process improvements resulting in greater H₂ utilization and, consequently, greater ethanol production.

Experiments were performed to measure the dependence of hydrogenase activity from Clostridium P11 on H₂ partial pressure. The data were fit with a variety of published hydrogenase rate laws and the Okura rapid-equilibrium rate law was found to best describe hydrogenase activity in Clostridium P11. A constant that regulates the effect of H₂ partial pressure on hydrogenase activity, K_H2, was determined to be independent of electron acceptor and to have a value of 0.31 atm, implying that H₂ must be supplied to syngas fermentation processes employing this bacterium at ~3 atm to maximize hydrogenase activity. K_BV and K_MV, constants that regulate the effect of benzyl viologen and methyl viologen (the electron acceptors used for the kinetic studies) on hydrogenase activity, were determined to be 1.7-2.4 mM and 10.6 mM, respectively.