Glutathione is the most biologically abundant low molecular weight intracellular thiol. By way of the reducing power of its free sulfhydral (-SH), glutathione plays a key role in many cellular processes. These involve protection of cells against oxidative stress, xenobiotics and radiation (reviewed by Sies, 1999 and Sen, 1997). Glutathione is synthesised intracellularly from its constituent amino acids by the consecutive action of two enzymes, γ-glutamylcysteine synthetase (γ-GCS) and glutathione synthetase (GS), with both reactions consuming ATP.
Method of action
Glutathione's main role as an antioxidant is the use of its sulfhydryl group as a nucleophilic scavenger and electron donor. However, glutathione has several other vital maintenance activities, including;
A cofactor in the function of several antioxidant enzymes, glutathione peroxidises, which are responsible for the degradation of peroxides.
Maintenance of ascorbate in its reduced state so it can remain an effective antioxidant/reducing agent. It does this through the activity of the glutathione-dependent enzyme dehydroascorbate reductase.
An essential component in an NADPH pathway that prevents cellular components from being oxidised. This function is essential for the maintenance of protein thiols, and the creation of deoxyribonucleotide precursors for DNA synthesis, through the reduction of ribonucleotides, (Meister, 1991).