Photoenzymatic Synthesis of l -Alanine with In Situ NADH Regeneration by Alkali Metal-Regulated Carbon Nitride

Abstract

The efficiency of photoenzymatic catalysis is often constrained by sluggish nicotinamide adenine dinucleotide (phosphate) [NAD(P)H] regeneration and unfavorable interactions among system components. Here, we report an ionic radius-engineered poly(heptazine imide) (PHI) photocatalyst, where Cs+ incorporation directs the formation of a highly crystalline carbon nitride framework with enhanced charge separation and interfacial reactivity. The resulting Cs-PHI achieves a high NADH regeneration rate of 0.30 mmol g−1 min−1, 5–8 times higher than the rates typically reported for PHI-based photocatalysts. Coupling this catalyst with alanine dehydrogenase from Bacillus subtilis (BsAlaDH) enables the reductive amination of pyruvate and ammonia to l-alanine under visible light, with systematic evaluation revealing that both pH and NH4+ ions critically modulate cofactor regeneration, which consequently impacts enzymatic reaction. This study demonstrates PHI as an effective strategy to integrate materials design with photoenzymatic system requirements. These insights, combined with operational windows for pH and substrate control, establish a robust platform for light-driven l-alanine synthesis.