Adenosine 5'-triphosphate γ-(1-[2-nitrophenyl]ethyl) ester (“Caged” ATP) is used as a photolyzing substrate of luciferase-mediated firefly bioluminescence and other ATP-dependent photolytic processes. Caged ATP has also been used to study the dynamics of ATP-driven linear molecular motors such as myosin Va. Caged ATP is used to study intracellular mechanisms; Irradiation with a short light pulse of 360 nm wavelength releases the parent compound from its cage resulting in a time- and quantity-specific concentration increase of ATP within the cell; Relaxation of muscle fibres by photolysis of caged ATP.