UC Riverside

Recently, several formate dehydrogenases have been reported to be able to catalyze the reduction of carbon dioxide to formic acid. The main challenge with these enzymes are that either the CO2-reducing activity is very low, or highly oxygen sensitive. In this dissertation, we employed an oxygen tolerant formate dehydrogenase (FdsABG) from Cupriavidus ncecator (formerly known as Ralstonia eutropha) for conversion CO2 to formic acid. We found that the enzyme is kinetically competent to catalyze the reverse reaction, i.e. reduction of CO2 to formate by NADH, with a kcat of 10 s-1. Accumulation of formate in the reverse reaction was quantitatively account for consumption of NADH. It showed that all molybdenum- and tungsten-containing formate dehydrogenases, and probably also formylmethanofuran dehydrogenases, operate via a simple hydride transfer mechanism and were effective in catalyzing the reversible interconversion of CO2 and formate. To make the reaction of CO2 reduction more efficient and cost effective, we cloned the full-length soluble formate dehydrogenase (FdsABG) from C. necator and expressed in E. coli with a His-tag fused to the N terminus of fdsG subunit, and this overexpression system has simplified the FdsABG purification compared to production from native C. necator. We further combined this engineered C. necator FdsABG with glucose dehydrogenase, for continuous electron donation to the reaction of converting CO2 to formate. In dynamic electrochemistry study of FdsABG, the bioelectrocatalysis system provided electrons to FdsABG for the reduction of CO2 to formate without the expensive reducing agent, NADH. This work provided a framework for studying the electron transfer mechanisms inside of this protein and developed a highly efficient biocatalytic process for transformation of CO2 to formate that has applications as fuel for formic acid fuel-cells.