L-Arginine-7-amido-4-methylcoumarin hydrochloride is primarily used in biochemical research as a fluorogenic substrate for studying enzyme activity, particularly proteases like trypsin and other arginine-specific enzymes. When the enzyme cleaves the amide bond in the compound, it releases 7-amino-4-methylcoumarin, which is highly fluorescent. This property allows researchers to monitor enzyme kinetics and activity in real-time, making it a valuable tool in enzymology and drug discovery. It is also employed in assays to screen for protease inhibitors, which are potential therapeutic agents for diseases involving abnormal protease activity.