Fig. 4.

Functional implications of MAO enzymes in cellular signaling pathways. MAO activity results in the production of aldehydes, ammonia and the reactive oxygen species (ROS) hydrogen peroxide (H₂O₂). ROS can be scavenged by antioxidative enzymes such as glutathione peroxidase (GPx), superoxide dismutase (SOD) and catalase. If the cellular anti-oxidative capacity is exhausted, ROS may cause unordered cell death. On the other hand, ROS second messenger signaling may alter the activity of mitogen-activated protein kinases (MAPK) or of transcription factors. These changes in turn are directly or indirectly via gene expression regulation (dashed arrows) relayed to the proteins that regulate cell proliferation (cyclin D) or apoptotic cell death (Bcl-2 proteins). Further information is found in the main text