Figure 1.

The synthesis of glutathione. Two synthetic reactions combine glutamic acid, cysteine, and glycine to form glutathione. First, the enzyme γ-glutamylcysteine synthetase (also called γ-glutamylcysteine ligase) catalyzes formation of the unique γ-glutamyl bond between glutamic acid and cysteine (shown by the dotted red circle). This reaction requires energy input from the hydrolysis of ATP. Glycine is then linked to γ-glutamylcysteine by the enzyme glutathione synthetase. This reaction also requires energy input derived from the hydrolysis of ATP. The enzyme catalyzing the first reaction, γ-glutamylcysteine synthetase, is inhibited by normal intracellular glutathione concentrations (interrupted blue arrow shows inhibition).