Glutathione

GLUTATHIONE:
  • Glutathione is a tripeptide made up of glutamate, cysteine and glycine (T-glutamyl-cysteinyl-glycine).
  • Glutathione is present in all mammalian cells except neurons. The sulphydryl (-SH) group of cysteine residue is the reactive portion of glutathione which can undergo oxidation and reduction.
  • Thus, glutathione may exist as the reduced (G-SH) or oxidized form (G-S-S-G) and can play a role in some oxidation-reduction reactions.
  • In oxidized form two molecules of glutathione are linked by disulfide bond.
  • Cysteine in glutathione act as reducing agent 
FUNCTIONS : -
  • It helps in keeping some enzyme in active state by preventing the oxidation of sulphydryl (-SH) group of enzyme.
  • It helps in detoxification of H2O2 by reducing it. Superoxide anion (O2) first converted to H2O2 by superoxide dismutase. 
  • Glutathione helps in membrane transport H2O2 is then reduced to H2O2 by glutathione perioxidase, a reaction requires reduced glutathione. Thus, glutathione scavenges free radicals and superoxide anion.
  • It helps in detoxification of xenobiotics by their conjugation (conjugation reaction).
  • Reduced form of glutathione (GSH) with a free sulphydryl (-SH) group serves as a redox buffer, regulating redox state of the cell.
  • Reduced glutathione is essential for maintaining the normal structure of RBCs and for keeping hemoglobin iron in ferrous state (prevents formation of methemoglobin).
  • It is involved in the transport of amino acids across the cell membane of kidney and intestine.
GLUTATHIONE PEROXIDASE:
  • Glutathione peroxidase is an enzyme that contains the selenium analog of cysteine (selenocysteine) at the active site.
  • Glutathione peroxidase is the general name of an enzyme family with peroxidase activity whose main biological role is to protect the organism from oxidative damage.
  • The biochemical function of glutathione peroxidase is to reduce lipid hydroperoxides to their corresponding alcohols and to reduce free hydrogen peroxide to water.
  • Glutathione reductase contains a flavoprotein containing FAD. 
  • Reduced glutathione removes H2O2 in a reaction catalyzed by glutathione peroxidase, an enzyme that contains the selenium analogue of cysteine (selenocysteine) at the active site.
Exam Question of:
  • Glutathione Serves as a vehicle for the transport of amino acids into some cells
  • Glutathione is a tripeptide 
  • Glutathione conjugates xenobiotics
  • Glutathione is co-factor of various enzymes
  • Glutathione scavenges free radicals and superoxide ions
  • Glutathione peroxidase contains Selenium
  • Glutathione reductase contains FAD
  • Selenium is found in the active site of glutathione peroxidase for its function
  • Cysteine in glutathione act as reducing agent
  • Glutathione helps in membrane transport
  • Glutathione consist of glutamate, cysteine and glycine

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