Glutathione synthetase (GSS) is the second enzyme in the glutathione biosynthesis pathway. GSS catalyses the condensation of gamma-glutamylcysteine and glycine to form glutathione. Defects in the GSS are the cause of glutathione synthetase deficiency aka GSS deficiency or 5-oxoprolinuria or pyroglutamic aciduria, which is a severe form characterized by an increased rate of hemolysis and defective function of the central nervous system.