Carbon Dots from d‑Cysteine and Citric Acid Increase the Activity of the Enzyme Laccase

Chiral carbon dots (CDots) attract extensive attention due to their promising application in the biological field. Their biological effects strongly depend on their chiral structure. Laccase (Lac) is a classic multicopper-containing polyphenol oxidase. The impact of the chirality of CDots on the Lac activity has not been fully emphasized and studied yet. Here, chiral CDots are prepared by thermal polymerization from l/d-cysteine (l/d-Cys) and citric acid (CA), where the obtained twins of chiral CDots possess all the same properties such as size, charge, and elemental content, except chirality. The d-CDots (256 μg mL^–1) could improve the catalytic activity of Lac (88%), while the l-CDots have no obvious effect on Lac at the same concentration. Based on the results of the Michaelis constant (K_m) and circular dichroism (CD) spectra, compared with l-CDots, the superior catalytic performance of d-CDots is due to the preferable combination toward Lac, resulting in the change of the α helix structure of Lac. Our work reveals the important implications for solving the problem of limited and selective regulation of enzyme activity.