Studying the H-transfer mechanism of the formic acid / CO2 conversion catalyzed by formate dehydrogenases.

M.V. SLABOCH; H. ELIZALDE; K.B. MENDOZA; C.D. BRONDINO; M.G. RIVAS; P.J. GONZÁLEZ

Rosario

Encuentro; L Reunión Anual de la SAB.; 2022

Sociedad Argentina de Biofísica

The massive use of fossil fuels and deforestation continue to promote the increase in atmospheric CO2, one of the main causes of global warming and the alteration and destruction of sensitive ecosystems. It is necessary to optimize the conversion of CO2 into value added products. A currently desired option is to develop processes for capturing atmospheric CO2 and coupling it to new technologies for the sustainable alternative fuels production, aiming to support the world´s population activities. One of the most investigated alternatives is the electrochemical conversion of CO2 into carbon compounds with a lower oxidation state. However, the main obstacle to developing a profitable process is the energetic efficiency, but also that current electro-reduction methods cannot fully control the final product obtained, since a mixture of compounds is generated. From this mixture, only some compounds can be used directly as fuels.Formate dehydrogenases (FdH) are oxidoreductases that depend on different cofactors to perform catalysis. Despite the notable structural differences among FdHs, all of them catalyze the same reaction: formate CO2 + 2e- + 2H+, hence, they could be used to convert CO2 into formic acid. In this work, the metal-free NAD-dependent FdH from Thiobacillus sp. and the Mo-dependent FdH-S from C. necator H16 were isolated. Kinetic characterization of both enzymes was carried out and the type of multi-substrate mechanism was verified. Then, using formate with natural isotopic abundance and 99% enriched with 2H in the alpha position, the kinetic isotope effect (KIE) was studied by comparing the rate constants (kCat) obtained in the temperature range 4-50 °C. The H/D KIEs produced moderate values (< 2.0) and proved to be temperature dependent, suggesting H-tunneling contribution at temperatures below 20 °C. The differences observed in the KIEs could serve to explain why the metal-dependent FdHs catalyze the reduction of CO2 to formate more efficiently.