Phospho-L-arginine is a phosphorylated form of L-arginine and a highly diffusible, high-energy metabolite and phosphagen involved in energy storage in invertebrates including crustaceans, insects, and Trypanosoma species. In the locust L. migratoria, phospho-L-arginine is found in the flight muscles, where it acts as both a buffer system and shuttle mechanism for high-energy phosphate. Measurement of phospho-L-arginine by 31P-NMR spectroscopy has been used to study invertebrate energy metabolism in vivo.