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Biochemistry

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Carbohydrates

Question
27 out of 40
 

False regarding GLUTATHIONE?(AIIMS May 2008)



A Converts hemoglobin to methemoglobin

B Causes sulphur conjugation

C Required for detoxification

D Cofactor for many enzymes

Ans. A Converts hemoglobin to methemoglobin(Ref. Harper’s Illustrated Biochemistry 26th edition pg. 611, 629–630)

a. Glutathione (γ-glutamyl-cysteinylglycine) is a tripeptideconsisting of glutamic acid, cysteine, and glycine.

b. Glutathione is commonly abbreviated GSH.

c. A number of potentially toxic electrophilic xenobiotics (such as certain carcinogens) are conjugated to the nucleophilic GSH. The enzymes catalyzing these reactions are called glutathione Stransferasesand are present in high amounts in liver cytosol and in lower amounts in other tissues.

d. If the potentially toxic xenobiotics were not conjugated to GSH, they would be free to combine covalently with DNA, RNA, or cell protein and could thus lead to serious cell damage.

e. GSH is an important defense mechanism against certain toxic compounds, such as some drugs and carcinogens.

f. If the levels of GSH in a tissue such as liver are lowered (as can be achieved by the administration to rats of certain compounds that react with GSH), then that tissue can be shown to be more susceptible to injury by various chemicals that would normally be conjugated to GSH.

g. Glutathione conjugates are subjected to further metabolism before excretion.

h. The glutamyl and glycinyl groups belonging to glutathione are removed by specific enzymes, and an acetyl group (donated by acetyl-CoA) is added to the amino group of the remaining cysteinyl moiety. The resulting compound is a mercapturic acid, a conjugate of L-acetylcysteine, which is then excreted in the urine.

GLUTATHIONE HAS OTHER IMPORTANT FUNCTIONS IN HUMAN CELLS APART FROM ITS ROLE IN XENOBIOTIC METABOLISM –

a. It participates in the decomposition of potentially toxic hydrogen peroxide in the reaction catalyzed by glutathione peroxidase.

b. It is an important intracellular reductant, helping to maintain essential SH groups of enzymes in their reduced state.

c. A metabolic cycle involving GSH as a carrier has been implicated in the transport of certain amino acids across membranes in the kidney.

Carbohydrates Flashcard List

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