Pathway: Detoxification of Reactive Oxygen Species
Reactions in pathway: Detoxification of Reactive Oxygen Species :
Detoxification of Reactive Oxygen Species
Reactive oxygen species such as superoxide (O2.-), peroxides (ROOR), singlet oxygen, peroxynitrite (ONOO-), and hydroxyl radical (OH.) are generated by cellular processes such as respiration (reviewed in Murphy 2009, Brand 2010) and redox enzymes and are required for signaling yet they are damaging due to their high reactivity (reviewed in Imlay 2008, Buettner 2011, Kavdia 2011, Birben et al. 2012, Ray et al. 2012). Aerobic cells have defenses that detoxify reactive oxygen species by converting them to less reactive products. Superoxide dismutases convert superoxide to hydrogen peroxide and oxygen (reviewed in Fukai and Ushio-Fukai 2011). Catalase and peroxidases then convert hydrogen peroxide to water.
Humans contain 3 superoxide dismutases: SOD1 is located in the cytosol and mitochondrial intermembrane space, SOD2 is located in the mitochondrial matrix, and SOD3 is located in the extracellular region. Superoxide, a negative ion, is unable to easily cross membranes and tends to remain in the compartment where it was produced. Hydrogen peroxide, one of the products of superoxide dismutase, is able to diffuse across membranes and pass through aquaporin channels. In most cells the primary source of hydrogen peroxide is mitochondria and, once in the cytosol, hydrogen peroxide serves as a signaling molecule to regulate redox-sensitive proteins such as transcription factors, kinases, phosphatases, ion channels, and others (reviewed in Veal and Day 2011, Ray et al. 2012). Hydrogen peroxide is decomposed to water by catalase, decomposed to water plus oxidized thioredoxin by peroxiredoxins, and decomposed to water plus oxidized glutathione by glutathione peroxidases (Presnell et al. 2013).
Humans contain 3 superoxide dismutases: SOD1 is located in the cytosol and mitochondrial intermembrane space, SOD2 is located in the mitochondrial matrix, and SOD3 is located in the extracellular region. Superoxide, a negative ion, is unable to easily cross membranes and tends to remain in the compartment where it was produced. Hydrogen peroxide, one of the products of superoxide dismutase, is able to diffuse across membranes and pass through aquaporin channels. In most cells the primary source of hydrogen peroxide is mitochondria and, once in the cytosol, hydrogen peroxide serves as a signaling molecule to regulate redox-sensitive proteins such as transcription factors, kinases, phosphatases, ion channels, and others (reviewed in Veal and Day 2011, Ray et al. 2012). Hydrogen peroxide is decomposed to water by catalase, decomposed to water plus oxidized thioredoxin by peroxiredoxins, and decomposed to water plus oxidized glutathione by glutathione peroxidases (Presnell et al. 2013).
Cells are subject to external molecular and physical stresses such as foreign molecules that perturb metabolic or signaling processes, and changes in temperature or pH. Cells are also subject to internal molecular stresses such as production of reactive metabolic byproducts. The ability of cells and tissues to modulate molecular processes in response to such stresses is essential to the maintenance of tissue homeostasis (Kultz 2005). Specific stress-related processes annotated here are cellular response to hypoxia, cellular response to heat stress, cellular senescence, HSP90 chaperone cycle for steroid hormone receptors (SHR) in the presence of ligand, response of EIF2AK1 (HRI) to heme deficiency, heme signaling, cellular response to chemical stress, cellular response to starvation, and unfolded protein response.
Individual cells detect and respond to diverse external molecular and physical signals. Appropriate responses to these signals are essential for normal development, maintenance of homeostasis in mature tissues, and effective defensive responses to potentially noxious agents (Kultz 2005). It is convenient, if somewhat arbitrary, to distinguish responses to signals involved in development and homeostasis from ones involved in stress responses, and that classification is followed here, with macroautophagy and responses to metal ions classified as responses to normal external stimuli, while responses to hypoxia, reactive oxygen species, and heat, and the process of cellular senescence are classified as stress responses. Signaling cascades are integral components of all of these response mechanisms but because of their number and diversity, they are grouped in a separate signal transduction superpathway in Reactome.