Thiols

Low-molecular-weight thiol compounds and their associated enzymatic recycling systems are responsible for the protection of cells against oxidative stress and the maintenance of an optimal intracellular redox state. In most eukaryotes, including helminths, glutathione (GSH, l-γ-glutamyl- l-cysteinylglycine) in conjunction with various enzymes, such as GSH reductase, GSH peroxidase, catalase, and superoxide dismutase, fulfills these important functions. Although the majority of parasites appears capable of GSH biosynthesis, many of them, in particular protozoans, lack an effective enzymatic equipment to protect themselves against reactive oxygen metabolites. Catalase and GSH peroxidase are often missing, but with the exception of anaerobic protozoa most parasites contain superoxide dismutase for removal of superoxide and use specialized enzymatic systems in their thiol redox and detoxification mechanisms (Fig. 1). Plasmodium falciparumuses a rather complex GSH- and thioredoxin...