Monday, May 30, 2011

Synthetic Fuels from CO by Tweaking Molybdenum Nitrogenase

Nitrogenase enzymes allow living organisms to convert atmospheric N2 to organic nitrogen, for growth, development, and metabolism. But Utah State University researchers have discovered that by tweaking molybdenum nitrogenease -- substituting an alanine or glycine in place of the normal valine in a particular position -- the resulting enzyme can do a lot more than convert N2.
...when the nitrogenase MoFe protein α-70Val 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 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. _Journal of Biological Chemistry _ via _USU PDF

It is unlikely that the yields are particularly high at this point -- and organic enzymes may well prove too delicate for high volume industrial synthesis of fuels from syngas-derived CO. In that case, biomimetic nano-catalysts are likely to be crafted which can take over for the nitrogenase enzyme.

More from USU:
While studying bacterial enzymes, known as nitrogenases, used in nitrogen reduction, Utah State University biochemists Zhi-Yong Yang and Lance Seefeldt, along with colleague Dennis Dean of Virginia Tech, discovered a molybdenum nitrogenase capable of converting carbon monoxide into usable hydrocarbons. The reaction is similar, they say, to FT synthesis.

“This is pretty profound,” says Seefeldt, professor in USU’s Department of Chemistry and Biochemistry. “Understanding this process paves the way for developing better ways of converting carbon monoxide, a toxic waste product of combustion, into transportation fuel and precursors for plastics — without the time and energy required for conventional extraction of fossil fuels.”

The scientists’ findings appear in the article “Molybdenum Nitrogenase Catalyzes the Reduction and Coupling of CO to Form Hydrocarbons,” in the June 3, 2011 issue (and May 27 online issue) of Journal of Biological Chemistry. The paper was selected as “Paper of the Week” by the journal’s editorial board, an honor bestowed on the top one percent of more than 6,600 manuscripts reviewed annually by the publication’s editors. In the “Paper of the Week” feature, Yang, a doctoral candidate mentored by Seefeldt, is highlighted as an up-and-coming researcher. _USU

Of course if the researchers focused on creating better nitrogenases for converting atmospheric N2 to organic nitrogen, the revolutionary impact on human society would be just as great as discovering a breakthrough in synthetic fuels production.

It is likely that both breakthroughs will be made in time, built upon the crucial work being done at USU and other labs around the world. If so, better nitrogenases will contribute to abundant food AND abundant fuel.

H/T GreenCarCongress

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