ATP plays an important role in energy exchange in biological systems. A lot of methods have been used for ATP determination. The most successful technique is the bioluminescent method. Luciferin is catalytically oxidized by the enzyme luciferase in a high quantum yield chemiluminescent reaction. Under optimum conditions, light intensity is lineary related to ATP concentration. ATP can be monitored by direct lysis of the cells with suitable detergent, the released ATP is then free to react with the luciferin-luciferase and leading to light emission at 562 nm. A luminometer can be used to measure the light intensity.