BioVision's Highly Stable Luciferase/Luciferin Reagent utilizes a genetically modified variant derived from the Luciferase of Diaphanes pectinealis (Chinese Firefly) endemic to Yunnan province, China. BioVision's luciferase (rLucHS) has been modified to provide enhanced stability compared to the normal phenotype of Photinus pyralis, as well as a broader and more physiologically relevant effective pH range. At all pHs below ~8.2, rLucHS is significantly more active than commercial Photinus pyralis luciferase and is stable for weeks at room temperature and >60 minutes at 37°C. The specific activity of rLucHS is ~ 5x10??RLU/mg protein. This reagent has application to measure ATP levels in a wide variety of biological samples such as cells,