Researchers have discovered a biochemical oxygen sensing system conserved across biological kingdoms, which allows both plant and animal cells to sense and respond appropriately to changes in oxygen levels - an ability central to the survival of most forms of life. The newly identified enzymatic oxygen sensor is functionally and biochemically identical in plants and animals. Because oxygen sensing is impaired in many human diseases, like cancer, the findings could pave the way to new therapeutic interventions for addressing cellular hypoxia (oxygen deficiency). In order for cells and tissues to adapt to hypoxic conditions, they must first be able to detect oxygen deficiencies. Previous research has shown that a transcription factor called hypoxia inducible factor (HIF) works as an oxygen sensor in humans. Other molecular hypoxia signaling systems have been identified across all four eukaryotic kingdoms; in plants, for example, plant cysteine oxidase enzymes control responses to hypoxia. Norma Masson and colleagues investigated this type of cysteine oxidation in animals and identified the enzyme cysteamine (2-aminoethanethiol) dioxygenase (ADO), which functions as an oxygen sensor in both animals and plants. Masson et al. suggest that ADO likely operates on a shorter timescale than HIF, producing more rapid responses to hypoxic conditions. Neither ADO nor HIF, however, is mutually exclusive - the results predict that both the ADO and HIF systems will interact to produce responses to hypoxia.