Forster Resonance Energy Transfer Study of the Improved Biocatalytic Conversion of CO2 to Formaldehyde by Coimmobilization of Enzymes in Siliceous Mesostructured Cellular Foams

By combining two enzymes, formate dehydrogenase (FateDH) and formaldehyde dehydrogenase (FaldDH), it is possible to drive the thermodynamically unfavorable conversion of CO2 to formaldehyde. For this purpose, the enzymes were coimmobilized in siliceous mesostructured cellular foams (MCFs). A high degree of adsorption of both enzymes was achieved by coimmobilizing the enzymes sequentially, i.e., first FateDH and then FaldDH. The highest conversion rate was obtained with an enzyme mass ratio of 1:15 (FateDH/FaldDH). Using MCF functionalized with mercaptopropyl groups (MCF-MP), the activity increased similar to 4 times compared to the enzymes free in solution. To probe the distance between the two enzymes, they were separately labeled with either Cy3 or Cy5 dyes and studied with Forster resonance energy transfer (FRET). An increased energy transfer was observed when the enzymes were coimmobilized in MCF-MP, suggesting that the two enzymes are in close proximity, resulting in higher conversion of CO2 to formaldehyde.