γ-glutamylcysteine

Structural formula
General
Surname	γ-glutamylcysteine
other names	(2 S ) -2-Amino-5 - {[(2 R ) -1-hydroxy-1-oxo-3-sulfanylpropan-2-yl] amino} -5-oxopentanoic acid γ-Glu-Cys γ-EC
Molecular formula	C 8 H 14 N 2 O 5 S
External identifiers / databases
CAS number 636-58-8 EC number 636-320-8 ECHA InfoCard 100.164.128 PubChem 123938 ChemSpider 110467 DrugBank DB03408 Wikidata Q288236
properties
Molar mass	250.27 g mol −1
Physical state	firmly
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 315-319-335 P: 261-305 + 351 + 338
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

γ-Glutamylcysteine (γ-EC) is a dipeptide made from the amino acids cysteine and glutamic acid . In many organisms it occurs as a preliminary stage in the formation of glutathione . In contrast to the normal peptide bond between amino acids, the amino group of cysteine ​​is not linked to the α- carboxy group of glutamic acid, but to the γ- carboxy group in the side chain . This unusual bond can not be cleaved by most peptidases and therefore gives γ-EC a high stability.

Biological importance

The thiol group of γ-glutamylcysteine ​​is less reactive than that in free cysteine ​​and therefore less sensitive to spontaneous oxidation . It is therefore assumed that the possibility of γ-glutamylcysteine ​​formation originally represented an evolutionary advantage, since γ-glutamylcysteine ​​is a better storage form for reduced sulfur than cysteine. A further reduction in the tendency towards spontaneous oxidation is achieved in the presence of low ion concentrations through the formation of glutathione. In organisms capable of glutathione synthesis, the γ-glutamylcysteine ​​concentration is therefore usually very low.

γ-glutamylcysteine ​​can dimerize to bis-γ-glutamylcysteine with oxidation and formation of a disulfide bridge and thus serve as a reducing agent . Halobacteria can synthesize γ-glutamylcysteine ​​but not glutathione. There is a NADPH -dependent bis-γ-glutamylcysteine ​​reductase , so that the γ-glutamylcysteine ​​/ bis-γ-glutamylcysteine ​​system can take on the role of the glutathione / GSSG system as an antioxidant . In these bacteria, γ-glutamylcysteine ​​concentrations are found in the low millimolar range.

biosynthesis

The synthesis of γ-glutamylcysteine ​​is catalyzed by the enzyme glutamate cysteine ​​ligase . The reaction is coupled with the splitting of a molecule of adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and phosphate :

+ + ATP     + + ADP + P _i ${\displaystyle \longrightarrow }$

Glutathione can then be formed via glutathione synthase by binding a glycine molecule to the cysteine ​​carboxy group of γ-glutamylcysteine.

swell

• Robert C. Fahey, Alfred R. Sundquist: Evolution of Glutathione Metabolism . In: Advances in Enzymology and Related Areas of Molecular Biology . tape 64 , 1991, pp. 1-53 (English).

Individual evidence

1. ↑ ^{a b} data sheet γ-Glu-Cys from Sigma-Aldrich , accessed on April 26, 2011 ( PDF ).
2. ^ Alfred R. Sundquist, Robert C. Fahey: The Function of y-Glutamylcysteine ​​and Bis-y-glutamylcystine Reductase in Halobacterium halobium . In: Journal of Biological Chemistry . tape 264 , no. 2 , 1989, pp. 719–725 (English, jbc.org [PDF]).