There are several isoforms of GPx, each encoded by different genes and having distinct tissue distributions and substrate specificities. The major isoforms include GPx1, GPx2, GPx3, and GPx4. GPx1 is ubiquitous and found in almost all tissues. GPx2 is mainly present in the gastrointestinal tract, GPx3 in plasma, and GPx4 in testis and other tissues.
