Glutathione Peroxidase (GPx) (EC 18.104.22.168) enzymes belong to a family of selenoproteins whose function is to catalyze the reduction of various peroxides. Four types of GPx (GPx-1 to 4) have been identified in mammalian species. GPx-1 is the classic intracellular form while GPx-2 to 4 are gastrointestinal, plasma and phospholipid hydroperoxide metabolizing forms respectively.
This assay is an adaptation of the method of Paglia and Valentine. Glutathione peroxidase (GPX) catalyzes the reduction of an organic peroxide (ROOH), oxidizing reduced glutathione (GSH) to form disulfde glutathione (GSSG). The oxidized glutathione is then reduced by glutathione reductase (GR) and b-nicotinamide adenine dinucleotide phosphate (NADPH) forming NADP+ (resulting in decreased absorbance at 340 nm) and recycling the GSH. Because glutathione peroxidase (GPx) is limiting, the decrease in absorbance at 340 nm is directly proportional to the glutthione (GPx) concentration.