A synergistic photoenzymatic catalytic system using threonine aldolases enables the efficient synthesis of α-tertiary amino acids from pyridinium salts and small amino acids with high enantioselectivity. This method involves the use of a Rose Bengal photoredox catalyst and PLP-dependent threonine aldolases. The strategy allows for the direct alkylation of unprotected alanine and glycine, producing various α-tertiary amino acids in a single step as a single enantiomer. UV–vis spectroscopy studies suggest a ternary interaction between the pyridinium salt, protein, and photocatalyst, which is hypothesized to localize radical formation to the active site. This method highlights the potential of combining photoredox catalysts with enzymes to reveal new catalytic functions for known enzymes. α-Tertiary amino acids are essential components of drugs and agrochemicals, but traditional syntheses are step-intensive and provide limited structural diversity with varying enantioselectivity. The new method overcomes these limitations by utilizing a synergistic approach involving photoredox catalysis and enzyme activity. The threonine aldolase catalyzes the formation of β-hydroxy-α-amino acids from small amino acids and aldehydes, with the pyridinium salt acting as an alkyl radical source. The Rose Bengal photoredox catalyst facilitates the generation of alkyl radicals through single-electron reduction, which are then used in the alkylation reaction. The method demonstrates broad substrate tolerance, successfully synthesizing various α-tertiary amino acids with high enantioselectivity. The reaction conditions were optimized to achieve high yields and excellent stereocontrol. The study also explores the use of different substrates, including electron-rich and sterically demanding arenes, and demonstrates the versatility of the system. The results show that the method can be applied to a wide range of substrates, including glycine, and can produce α-tertiary amino acids with high enantioselectivity. The mechanism of the reaction involves the formation of a quinonoid intermediate, which is crucial for the catalytic activity of the threonine aldolase. The interaction between the pyridinium salt, Rose Bengal, and the enzyme is essential for localizing radical formation to the active site. The study also investigates the binding of the photocatalyst to the enzyme and the role of the quinonoid intermediate in the reaction. The results suggest that the ternary interaction between the pyridinium salt, Rose Bengal, and the enzyme is responsible for the high enantioselectivity observed in the reaction. This work demonstrates the potential of combining photoredox catalysis with enzymes to develop new catalytic strategies for the synthesis of complex molecules. The method provides a promising approach for the efficient and selective synthesis of α-tertiary amino acids, which are important in pharmaceutical and agA synergistic photoenzymatic catalytic system using threonine aldolases enables the efficient synthesis of α-tertiary amino acids from pyridinium salts and small amino acids with high enantioselectivity. This method involves the use of a Rose Bengal photoredox catalyst and PLP-dependent threonine aldolases. The strategy allows for the direct alkylation of unprotected alanine and glycine, producing various α-tertiary amino acids in a single step as a single enantiomer. UV–vis spectroscopy studies suggest a ternary interaction between the pyridinium salt, protein, and photocatalyst, which is hypothesized to localize radical formation to the active site. This method highlights the potential of combining photoredox catalysts with enzymes to reveal new catalytic functions for known enzymes. α-Tertiary amino acids are essential components of drugs and agrochemicals, but traditional syntheses are step-intensive and provide limited structural diversity with varying enantioselectivity. The new method overcomes these limitations by utilizing a synergistic approach involving photoredox catalysis and enzyme activity. The threonine aldolase catalyzes the formation of β-hydroxy-α-amino acids from small amino acids and aldehydes, with the pyridinium salt acting as an alkyl radical source. The Rose Bengal photoredox catalyst facilitates the generation of alkyl radicals through single-electron reduction, which are then used in the alkylation reaction. The method demonstrates broad substrate tolerance, successfully synthesizing various α-tertiary amino acids with high enantioselectivity. The reaction conditions were optimized to achieve high yields and excellent stereocontrol. The study also explores the use of different substrates, including electron-rich and sterically demanding arenes, and demonstrates the versatility of the system. The results show that the method can be applied to a wide range of substrates, including glycine, and can produce α-tertiary amino acids with high enantioselectivity. The mechanism of the reaction involves the formation of a quinonoid intermediate, which is crucial for the catalytic activity of the threonine aldolase. The interaction between the pyridinium salt, Rose Bengal, and the enzyme is essential for localizing radical formation to the active site. The study also investigates the binding of the photocatalyst to the enzyme and the role of the quinonoid intermediate in the reaction. The results suggest that the ternary interaction between the pyridinium salt, Rose Bengal, and the enzyme is responsible for the high enantioselectivity observed in the reaction. This work demonstrates the potential of combining photoredox catalysis with enzymes to develop new catalytic strategies for the synthesis of complex molecules. The method provides a promising approach for the efficient and selective synthesis of α-tertiary amino acids, which are important in pharmaceutical and ag