ABSTRACT
Exposure of mammalian cells to light results in the photochemical generation
of reactive oxygen species, such as singlet oxygen1 or superoxide,2 with the
potential of causing oxidative damage. Several cellular lines of defense exist to
cope with this challenge, but the tripeptide glutathione appears to play a prominent
role in the cellular response to a stressful stimulus with an oxidative component;
for example, there is ample evidence that age-related nuclear cataract is linked to
oxidative processes and apparently affected by cellular glutathione levels.3,4
GLUTATHIONE
Glutathione, or g-glutamylcysteinylglycine (GSH), is the major thiol of low molecular mass present in mammalian cells, with concentrations usually in the
millimolar region. It is involved in the cellular antioxidant defense as part of a
network of enzymes (Figure 1) that use GSH as the supplier of electrons for the
reduction of peroxides (glutathione peroxidases), that keep glutathione in its
reduced state (glutathione reductase) and that covalently couple GSH to various
electrophilic compounds in phase II drug metabolism (glutathione S-transferases).
Due to its high intracellular concentrations, the cellular redox state is governed to a
large extent by the glutathione redox status.
