Amino acids from the air
Chemists from Germany have learned how to turn air into protein "manna"
German biochemists have discovered an enzyme that can directly convert atmospheric carbon dioxide and alcohol into molecules of methionine, one of the key "molecules of life". The results of their experiments were published in the journal Nature Catalysis.
"Compared to photosynthesis, the closest natural analogue of this process, our idea looks very simple and elegant. About 14 different enzymes are involved in photosynthesis, and its efficiency usually reaches 20%, whereas our approach requires the use of only two protein catalysts," said Arne Skerra from the Technological University of Munich (Germany).
In recent years, scientists have been trying to find a way to convert atmospheric CO2 into biofuels and other useful substances. For example, last July, physicists from Chicago created a solar battery that directly uses light energy to split CO2 and produce carbon monoxide and hydrogen. A few months later, their colleagues from the National Laboratory in Oak Ridge created a catalyst that converts carbon dioxide into ethanol, "ordinary" alcohol.
All these catalysts and systems of "transmutation" of air into alcohol and other useful organic substances can help not only solve the problem of providing humanity with green fuel, but also find cheaper sources of raw materials for the chemical industry.
Skerra and his colleagues added to their number a combination of two protein molecules that convert carbon dioxide into the simplest "bricks of life", amino acids, experimenting with enzymes that yeast and some other microbes use to convert the latter into various alcohols.
This process was discovered back in 1903 by the famous German chemist Felix Ehrlich, and since then scientists have been trying to adapt it for the production of various alcohols, as well as revealing the secrets of what substances in vodka and other alcoholic beverages can aggravate a hangover.
The authors of the article noticed that many of the enzymes involved in the work of the "Ehrlich chain" can be forced to accelerate the reverse reactions by slightly changing their structure. Guided by this idea, scientists tried to force two similar proteins not to decompose amino acids into alcohols and carbon dioxide, but rather to assemble their molecules from these components.
Initially, according to Skerra himself, his team did not have much hope for such reactions, since, as scientists believed, they should have occurred only at high concentrations of CO2 and at very high pressures. The first experiments unexpectedly showed that similar transformations occur at relatively normal pressures and fractions of carbon dioxide in the air.
More advanced versions of enzymes were able to reach a fantastically high level of efficiency for such reactions – more than 40%. Scientists suggest that computer modeling will help them make this reaction even more efficient and suitable for industrial applications.
Methionine, as the researchers note, is now used as a food additive for poultry and livestock, which makes its production profitable even at the current stage of technology development. Similarly, according to biochemists, it is possible to produce many other critically important amino acids, such as isoleucine and leucine (they have already received these amino acids: “Similarly, L-leucine and L-isoleucine were prepared via biocatalytic carboxylation of 3- or 2-methylbutanal, respectively” – VM), which in theory it will allow you to get food and vitamins directly from the air, using only water, carbon dioxide and similar catalysts.
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