The following are major free radical scavengers except:
Ans. D. Glutamine. (Ref. Harper Biochemistry 28th/ pg. 483; Robbin's 8th/pg. 20, 21; Table 1-3; Fig. 1-20)A series of enzymes acts as free radical-scavenging systems and breaks down H202 include the following:# Superoxide dismutases (SODs) ----- Option A----- are found in many cell types and convert oxygen free radical to H2O2.# Catalase, ---- Option B---- present in peroxisomes, decomposes H2O2 (2H2O2 ? 02 + 2H2O).# Glutathione peroxidase---- Option C---- also protects against injury by catalyzing free radical breakdown(H2O2 + 2GSH? GSSG + 2H2O, or 2OH + 2GSH ? GSSG + 2H2O). The intracellular ratio of oxidized glutathione (GSSG) to reduced glutathione (GSH) is a reflection of the oxidative state of the cell and is an important indicator of the cell's ability to detoxify ROS.REMOVAL OF FREE RADICALS:The principle free radicals (reactive Oxygen species) involved in cell injury are:# Superoxide dismutase (SOD):- in mitochondria- Converts O2 (superoxide) a H2O2.# Catalase- In peroxisomes- Converts H2O2 a H2O + O2.# Glutathione Peroxidase- in mitochondria.- Converts "OH (hydroxyl radical) a H2O2 a H2O + O2.# Peroxiredoxins- Cause conversion to HNO2.- In cytosol and mitochondria.Antioxidants either block the initiation of free radical formation or inactivate (e.g., scavenge) free radicals. Examples:# Lipid-soluble vitamins E and A as well as Vit C and glutathione in the cytosol.# Iron and copper can catalyze the formation of ROS. The levels of these reactive metals are minimized by binding of the ions to storage and transport proteins (e.g., transferrin, ferritin, lactoferrin, and ceruloplasmin), thereby minimizing the formation of ROS.GENERATION OF FREE RADICALS:Inflammation, radiation, O2 toxicity, chemicals and reperfusion injury results in free radical formation, wherein following are mainly involved:# NADPH oxidase,# Oxidases in peroxisomes# Superoxide dismutase (SOD),# NO synthase and# Generation from H2O by hydrolysis .Free radicals may be generated within cells in several ways# The reduction-oxidation reactions that occur during normal metabolic processes.# Absorption of radiant energy (e.g., ultraviolet light, x-rays).# Rapid bursts of ROS are produced in activated leukocytes during inflammation. This occurs by a precisely controlled reaction in a plasma membrane multiprotein complex that uses NADPH oxidase for the redox reaction (i.e. oxidative burst in phagocytes).# Enzymatic metabolism of exogenous chemicals or drugs# Transition metals such as iron and copper# Nitric oxide (NO), an important chemical mediator generated by endothelial cells, macrophages, neurons, and other cell types, can act as a free radical and can also be converted to highly reactive peroxynitrite anion (ONOO-) as well as NO2 and NO3.
Superoxide dismutase
Catalase
Glutathione
Glutamine
Enzymes