L,L-Dityrosine（Cat No.:I018300）is a dimeric amino acid formed by oxidative cross-linking of two tyrosine residues through a covalent carbon–carbon bond between their phenolic rings. It naturally occurs in proteins under oxidative stress or enzymatic modification, serving as a biomarker for protein oxidation and tissue damage. L,L-Dityrosine contributes to structural stabilization in extracellular matrix proteins and has been studied in aging, neurodegenerative disorders, and oxidative stress-related diseases. As a biochemical tool, it is used to investigate protein cross-linking, free radical activity, and mechanisms of oxidative damage in biological systems.