Figure 3.

γ-Glutamyl cycle. Glutathione (GSH) is synthesized from glutamine and cysteine by γ-glutamylcysteine synthetase (GS) and glutathione synthetase (GSS) during the γ-glutamyl cycle. In patients with glutathione synthetase deficiency (GSD), the reduction in GS activity leads to the intracellular accumulation of γ-glutamylcysteine, which is converted to 5-oxoproline (OXP) and cysteine, with the resultant increase in 5-OXP concentration in blood and urine. This figure was created by Satoshi Ekuni, based on data from Ristoff E, Larsson A. Inborn errors in the metabolism of glutathione. Orphanet J Rare Dis 2007; 2: 16.