Glutathione pathway

Glutathione synthetase (EC 6.3.2.3 GSH-S) mediates the second step in the synthesis of GSH, by the addition of glycine to the dipeptide y-glutamylcysteine. The protein is a homodiraer of 52kDa.  

The gene for GSH-S is located on chromosome 20qll.2 and contains 12 exons spanning 23 

In the few cases that have been described, mild chronic hemolytic anemia is associated with deficiency of GSH-S/ The disorder is inherited in an autosomal recessive mode. Such people may also have more severe acute hemolytic crises when exposed to redox substances, such as 8-amino-quinolines or other oxidant drugs. 

There are two distinct types of GSH-S deficiency, both associated with mild chronic hemolysis in one type, hemolysis is the only clinical manifestation. In the other, the major clinical features are mental retardation, severe generalized muscle weakness, tremors, incoordination, hemolytic anemia, and metabolic acidosis. This second and much more severe type of GSH-S deficiency is also known as 5-oxopro-linurta or pyroglutamic aciduria. The difference in severity of these disorders reflects the fact that in the mild form, GSH-S deficiency is confined to the RBCs because in this disorder the GSH-S is unstable. GSH-S activity is present in adequate quantity in young RBCs, but it rapidly declines as the cells age, because the cells are unable to synthesize new molecules of GHS-S. Other cells of the body that have nuclei and ribosomes can compensate for accelerated denaturation of GSH-S by synthesizing more. On the other hand, in the severe systemic form of GSH-S deficiency, aE cells of the body have low activities of GSH-S because they cannot form this enzyme in adequate amounts. In both types of GSH-S deficiency, RBCs exhibit notable reduction in GSH concentration. 

Several mutations in the gene have been identified recently, associated with the disease. The majority of the mutations are missense, two small deletions and one splice site mutation.  

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L-2-oxothiazolidine-4-carboxylic acid (OTCA) (4+5 mmol/kg) enhanced glutathione availability and increased excretion of urinary mercapturic acid at the higher doses. These results suggest that OTCA increases the capacity for detoxification via the glutathione pathway. 

Early studies suggested that the relative activities of each pathway could be determined by measuring exhaled carbon monoxide (or carboxyhaemoglobin in blood) and carbon dioxide, resulting from the P450 and glutathione pathways respectively. How-... 

Dringen R, Hirrlinger J. 2003. Glutathione pathways in the brain. Biol Chem 384 505-516. 

A number of these enzymes are expressed in other tissues as well but cause a notable deficiency predominantly in red blood cells because of the life span of the erythrocyte after the loss of protein synthesis. Once an enzyme is degraded or otherwise becomes nonfunctional, it cannot be replaced by new or other compensating proteins because of the lack of nucleus, mitochondria, ribosomes, and other cell organelles in mature red cells. Disorders have been described in the EMP, HMP, Rapoport-Luebering cycle, the glutathione pathway (Figure 21-9), purine-pyrimidine metabolism and methemoglobin reduction. 

Figure 21-9 Interrelationship of hexose monophosphate and glutathione pathways. GSH, Reduced glutathione GSSG, oxidized glutathione.

Glutathione reductase (EC 1.8.1.7 formerly EC 1.6.4.2 GSR) links the glutathione pathway to the hexose monophosphate pathway through the reversible oxidation and reduction of NADP. Flavin adenine dinucleotide (FAD) is necessary as a cofactor. The enzyme maintains high levels of reduced glutathione in the cell. Two isoforms exist, a mitochondrial and cytoplasmic form, produced by alternative initiation. The molecule is a homodimer, linked by a disulfide bridge. Each subunit (522 amino acids 56kDa) is divided into four domains of which domains one and two bind FAD and NADPH, respectively and domain four forms the interface. ... 

Chromatography on polyglycoside based DEAE and QAE anion exchangers has also been used successfully for the Isolation of various glutathionate pathway metabolites (45-48). Figure 4 demonstrates the separation of this type of metabolites of methidathion produced by rat liver in-vitro experiments (47). 

Faucet-Marquis, V., Pont, F., Stormer, F.C., Rizk, T., Castegnaro, M. Rohl-Leszkowicz, A. (2006) Evidence of a new dechlorinated ochratoxin A derivative formed in opossum kidney cell cultures after pretreatment by modulators of glutathione pathways correlation with DNA adduct formation. Mol. Nutr. Food Res. 50, 530-542. 

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