Molybdenum nitrogenase catalyzes the reduction and coupling of CO to form hydrocarbons

Abstract

The molybdenum-dependent nitrogenase catalyzes the multi-electron reduction of protons and N2 to yield H2 and 2NH3. It also catalyzes the reduction of a number of non-physiological doubly and triply bonded small molecules (e.g. C2H2, N2O). Carbon monoxide (CO) is not reduced by the wild-type molybdenum nitrogenase but instead inhibits the reduction of all substrates catalyzed by nitrogenase except protons. Here, we report that when the nitrogenase MoFe protein α-Val70 residue is substituted by alanine or glycine, the resulting variant proteins will catalyze the reduction and coupling of CO to form methane (CH4), ethane (C2H6), ethylene (C2H4), propene (C3H6), and propane (C3H8). The rates and ratios of hydrocarbon production from CO can be adjusted by changing the flux of electrons through nitrogenase, by substitution of other amino acids located near the FeMo-cofactor, or by changing the partial pressure of CO. Increasing the partial pressure of CO shifted the product ratio in favor of the longer chain alkanes and alkenes. The implications of these findings in understanding the nitrogenase mechanism and the relationship to Fischer-Tropsch production of hydrocarbons from CO are discussed. © 2011 by The American Society for Biochemistry and Molecular Biology, Inc.