A Hybrid Photo/Biocatalytic System for the Sustainable Synthesis of L-Alanine From Urea and Pyruvate

Developing sustainable routes to biodegradable polymers from renewable feedstocks is key to reducing reliance on petroleum and mitigating environmental pollution. Amino acids, such as L-alanine, are valuable monomers for biodegradable nylons. Artificial photosynthesis has recently been applied to amino acid synthesis, yet the use of biomass-derived nitrogen sources such as urea in visible-light driven L-alanine synthesis has not yet been explored. Here, we present a novel artificial photosynthetic system that converts urea and pyruvate, both biomass-derived compounds, into L-alanine under visible light. In this system, a visible light-driven NADH regeneration system consisting of triethanolamine (TEOA), zinc meso-tetra(4-sulfonatophenyl)porphyrin tetrasodium salt (ZnTPPS^4-), and pentamethylcyclopentadienyl (Cp*) rhodium 2,2'-bipyridine (bpy) ([Cp*Rh(bpy)(H₂O)]²⁺) is integrated with urease (URE), hydrolyzes urea into ammonia, and L-alanine dehydrogenase (AlDH), catalyzes the reductive amination of pyruvate. Under irradiation, the system produced 0.85 mM L-alanine after 24 h (85% yield based on pyruvate). This work represents the first exploration of urea-based, visible-light powered enzymatic L-alanine synthesis, offering a sustainable route to biodegradable polymer precursors from renewable nitrogen and carbon sources.