Gamma-L-Glutamyl-L-cysteine

• (2S )-2- amino-5- {[( 2R) -1-hydroxy -1-oxo -3- Monothioglycerol -2-yl ] amino} - 5 - oxopentanoic acid
• γ -Glu -Cys
• γ -EC

Fixed

Attention

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γ -glutamylcysteine ​​( γ -EC) is a dipeptide of the amino acids cysteine ​​and glutamic acid. In many organisms, it happens as a precursor in the formation of glutathione. In contrast to normal peptide bond between amino acids in this case the amino group of the cysteine ​​residue is not linked to the α -carboxyl group of glutamic acid but with the γ -carboxyl group in the side chain. This unusual binding can not be digested by most peptidases and confers γ -EC, therefore, a high stability.

Biological Significance

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

γ -glutamylcysteine ​​may be oxidation and formation of a disulfide bridge to dimerize bis- γ -glutamylcysteine ​​, and therefore serve as a reducing agent. Halo bacteria but γ -glutamylcysteine ​​not synthesize glutathione. Here there is a NADPH-dependent reductase bis- γ -glutamylcysteine ​​, so that the γ-Glutamylcystein/Bis-γ-Glutamylcystein-System the role of the glutathione / GSSG system can take over here as an antioxidant. These bacteria are found γ -glutamylcysteine ​​concentrations in the low millimolar range.

Biosynthesis

The synthesis of γ -glutamylcysteine ​​is catalyzed by the enzyme Glutamatcysteinligase. The reaction is coupled to the cleavage of a molecule of adenosine triphosphate ( ATP) to adenosine diphosphate (ADP ) and phosphate:

ATP ADP Pi

About the Glutathionsynthase can by binding a Glycinmoleküls to the cysteine ​​- carboxyl group of the γ - glutamylcysteine ​​be subsequently formed glutathione.

Swell

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