Photo-lysine hydrochloride is primarily used in biochemical research as a photoactivatable amino acid. It allows scientists to study protein interactions and dynamics by incorporating it into proteins, which can then be activated by light to form cross-links with nearby molecules. This property is particularly useful in mapping protein-protein interactions, understanding protein folding, and investigating cellular processes in real-time. Additionally, it serves as a tool in proteomics to identify and analyze protein complexes and their functional roles within cells. Its light-sensitive nature makes it a valuable reagent in advanced photochemical and biophysical studies.