γ-glutamylcysteine
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Surname | γ-glutamylcysteine | |||||||||||||||||||||
other names |
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Molecular formula | C 8 H 14 N 2 O 5 S | |||||||||||||||||||||
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properties | ||||||||||||||||||||||
Molar mass | 250.27 g mol −1 | |||||||||||||||||||||
Physical state |
firmly |
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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 :
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
- ↑ a b data sheet γ-Glu-Cys from Sigma-Aldrich , accessed on April 26, 2011 ( PDF ).
- ^ 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]).