Substrate Promiscuity of Thermoplasma acidophilum Malic Enzyme for CO₂ Fixation Reaction

CO₂ fixation technology has gained attention as a method to effectively utilize the abundant CO₂ in the atmosphere by converting it into useful chemicals. However, since CO₂ is a highly stable molecule, many of the currently developed methods for chemical CO₂ fixation require harsh conditions and reactive reagents. The establishment of efficient and sustainable processes is eagerly awaited. In this study, we investigated a biocatalytic process and achieved a carboxylation reaction under mild conditions (37 °C, 0.1 MPa CO₂) using a biocatalyst, Thermoplasma acidophilum NADP⁺-malic enzyme (TaME), and gaseous CO₂ by coupling enzymatic coenzyme regeneration. We also demonstrated for the first time that the carboxylation reaction by ME proceeds not only with pyruvate, a natural substrate, but also with 2-ketoglutarate.