AO (Amine Oxidase) is a group of enzymes that catalyze the oxidation of amine compounds, primarily including Polyamine Oxidase (PAO) and Monoamine Oxidase (MAO). They consist of multiple functional domains and are mainly located in the mitochondria and cytoplasm. AO plays a crucial role in regulating intracellular levels of polyamines and monoamines, controlling the degradation of neurotransmitters, and participating in cellular stress responses. The expression of AO family members is tissue-specific, and mutations or dysregulation in their genes are associated with various diseases, including neurodegenerative diseases, cardiovascular diseases, and cancer. The activity of AO is regulated by various factors, influencing the physiological state and adaptability of cells.