Cytosolic prostaglandin E synthase -cPGES) is a glutathione-dependent enzyme with a predicted size of 18.6 kDa. cPGES was first identified as an Hsp90-binding protein and named p23 for the size to which the protein migrated on a SDS-PAGE gel. cPGES is thought to modulate Hsp90 activity during the last stages of the chaperoning pathway. Since its identification as a cochaperone, cPGES was independently cloned, expressed and shown to have PGES activity, catalyzing the isomerization of PGH2 to PGE2. This enzyme is expressed in a variety of tissues and cells and its levels are unaffected by treatment with interleukin-1.beta. and tumor necrosis factor-.alpha.. Studies have shown multiple post-translational modifications that affect the activity of the protein.