Oxygen (O2) (O2)

Oxygen is a fundamental diatomic molecule (O2) essential for the survival of aerobic organisms, serving as the primary electron acceptor in the mitochondrial electron transport chain to drive ATP synthesis (Molecular Biology of the Cell, 2002). Beyond its metabolic role, intracellular oxygen levels act as a critical signaling variable that governs cellular adaptation to environmental changes through the regulation of Hypoxia-Inducible Factors (HIFs) (Semenza, 2012). The sensing of intracellular oxygen is primarily mediated by prolyl hydroxylase domain (PHD) enzymes, which utilize oxygen to hydroxylate HIF subunits, leading to their degradation under normoxic conditions. In the absence of sufficient oxygen (hypoxia), HIF stabilizes and translocates to the nucleus to activate genes involved in angiogenesis, erythropoiesis, and metabolic reprogramming (NIH, 2021). Therapeutically, oxygen is administered as a medical gas to correct hypoxemia, treat carbon monoxide poisoning, and enhance wound healing in hyperbaric chambers (WHO, 2021). However, maintaining precise intracellular oxygen levels is vital, as hyperoxia can trigger the excessive generation of reactive oxygen species (ROS), resulting in oxidative stress and significant cellular injury (StatPearls, 2023).

Other names

Molecular oxygenDioxygenIntracellular oxygenCellular oxygen

Oxygen acts as the terminal electron acceptor in the mitochondrial electron transport chain (ETC), facilitating the production of adenosine triphosphate (ATP) through oxidative phosphorylation (StatPearls, 2023). It also serves as a critical co-substrate for prolyl hydroxylase domain (PHD) enzymes, which hydroxylate Hypoxia-Inducible Factor (HIF) subunits in the presence of sufficient oxygen, thereby marking them for proteasomal degradation and regulating the cellular response to oxygen tension (Semenza, 2012).