Mitigation of Light‐Triggered Amine Transaminase Inactivation Through Immobilization on Boronic‐Functionalized Supports

ABSTRACT Recent studies reveal that PLP‐dependent amine transaminases are prone to light‐induced inactivation due to cofactor‐triggered conformational changes. To overcome this limitation, we herein develop a robust and broadly applicable strategy to prevent photoinactivation of PLP‐dependent transaminases. Our results show that both HEPES buffer and light exposure are the most detrimental factors affecting the stability of the transaminase from Pseudomonas fluorescens ( Pf ATA), leading to enzyme inactivation across all tested PLP concentrations. To overcome this limitation, we explored enzyme immobilization on both translucent and opaque supports functionalized with boronic groups. This support functionalization absorbs PLP and acts as a light quencher, avoiding PLP photodegradation and extending the Pf ATA operational half‐life by a factor of four compared to its free counterpart. Finally, by utilizing this immobilization chemistry, we developed a self‐sufficient heterogeneous biocatalyst (ssHB) by co‐immobilizing Pf ATA, formate dehydrogenase, and L‐alanine dehydrogenase, as well as the PLP and NADH cofactors, to aminate benzaldehyde with ammonium via a transamination/reductive amination cascade. This ssHB enables quantitative aldehyde amination in the first reaction cycle without the need for exogenous cofactor supply under ambient light conditions. Recycling of the three enzymes and the two cofactors was, however, limited, encouraging the further optimization of the multi‐enzyme/cofactor immobilized system.