TY  - JOUR
A1  - Schwarz, Fabian M.
A1  - Schuchmann, Kai
A1  - Müller, Volker
T1  - Hydrogenation of CO₂ at ambient pressure catalyzed by a highly active thermostable biocatalyst
T2  - Biotechnology for biofuels
N2  - Background: Replacing fossil fuels as energy carrier requires alternatives that combine sustainable production, high volumetric energy density, easy and fast refueling for mobile applications, and preferably low risk of hazard. Molecular hydrogen (H2) has been considered as promising alternative; however, practical application is struggling because of the low volumetric energy density and the explosion hazard when stored in large amounts. One way to overcome these limitations is the transient conversion of H2 into other chemicals with increased volumetric energy density and lower risk hazard, for example so-called liquid organic hydrogen carriers such as formic acid/formate that is obtained by hydrogenation of CO2. Many homogenous and heterogenous chemical catalysts have been described in the past years, however, often requiring high pressures and temperatures. Recently, the first biocatalyst for this reaction has been described opening the route to a biotechnological alternative for this conversion.
Results: The hydrogen-dependent CO2 reductase (HDCR) is a highly active biocatalyst for storing H2 in the form of formic acid/formate by reversibly catalyzing the hydrogenation of CO2. We report the identification, isolation, and characterization of the first thermostable HDCR operating at temperatures up to 70 °C. The enzyme was isolated from the thermophilic acetogenic bacterium Thermoanaerobacter kivui and displays exceptionally high activities in both reaction directions, substantially exceeding known chemical catalysts. CO2 hydrogenation is catalyzed at mild conditions with a turnover frequency of 9,556,000 h−1 (specific activity of 900 µmol formate min−1 mg−1) and the reverse reaction, H2 + CO2 release from formate, is catalyzed with a turnover frequency of 9,892,000 h−1 (930 µmol H2 min−1 mg−1). The HDCR of T. kivui consists of a [FeFe] hydrogenase subunit putatively coupled to a tungsten-dependent CO2 reductase/formate dehydrogenase subunit by an array of iron–sulfur clusters.
Conclusions: The discovery of the first thermostable HDCR provides a promising biological alternative for a chemically challenging reaction and might serve as model for the better understanding of catalysts able to efficiently reduce CO2. The catalytic activity for reversible CO2 hydrogenation of this enzyme is the highest activity known for bio- and chemical catalysts and requiring only ambient temperatures and pressures. The thermostability provides more flexibility regarding the process parameters for a biotechnological application.
KW  - Hydrogen production
KW  - Hydrogen storage
KW  - Carbon capture
KW  - Biohydrogen
KW  - Formate dehydrogenase
KW  - Hydrogenase
KW  - Hydrogen-dependent CO2 reductase
KW  - Thermophiles
KW  - Thermoanaerobacter kivui
Y1  - 2018
UR  - http://publikationen.ub.uni-frankfurt.de/frontdoor/index/index/docId/47189
UR  - https://nbn-resolving.org/urn:nbn:de:hebis:30:3-471897
SN  - 1754-6834
N1  - Open Access: This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
VL  - 11
IS  - Art. 237
SP  - 1
EP  - 11
PB  - BioMed Central
CY  - London
ER  -