Loading....
Coupon Accepted Successfully!

Biochemistry

Open Flashcards

Carbohydrates

Question
25 out of 40
 

All are true about glutathione except: (AIIMS Nov 2008)

 

 
A Converts hemoglobin to methemoglobin
B Decreases free radicals
C Helps in conjugation
D Cofactor of various enzymes.
Ans. A Converts hemoglobin to methemoglobin

Superoxide dismutase, catalase, glutathione protect blood cells from oxidative stress and damage so it es free radicals.


Conjugation with glutathione

Glutathione (γ -glutamyl-cysteinyl glycine) is a tripeptide consisting of glutamic acid, cysteine, and glycine. Glutathione is commonly abbreviated GSH (because of the sulfhydryl group of its cysteine, which is the business part of the molecule). A number of potentially toxic electrophilic xenobiotics (such as certain carcinogens) are conjugated to the nucleophilic GSH in reactions that can be represented as follows:

 

R + GSH àR – S- G

Where R = an electrophilic xenobiotic. The enzymes catalyzing these reactions are called glutathione S-transferase.

Glutathione has other important functions inhuman 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. The first reaction of the cycle is shown below.

Amino acid + GSH γ - Glutamyl amino acid + Cysteinyl glycine

This reaction helps transfer certain amino acids across the plasma membrane, the amino acid being subsequently hydrolyzed from its complex with GSH and the GSH being resynthesized from cysteinyl glycine. The enzyme catalyzing the above reaction is γ- glutamyltransferased (GGT). It is present in the plasma membrane of renal tubular cells and bile ductule cells, and in the endoplasmic reticulum of hepatocytes. The enzyme has diagnostic value because it is released into the blood from hepatic cells in various hepatobiliarydisease.

Carbohydrates Flashcard List

40 flashcards
1)
2)
3)
4)
5)
6)
7)
8)
9)
10)
11)
12)
13)
14)
15)
16)
17)
18)
19)
20)
21)
22)
23)
24)
25)
26)
27)
28)
29)
30)
31)
32)
33)
34)
35)
36)
37)
38)
39)
40)