Isomerase that catalyzes the conversion of PGH2 into the more stable prostaglandin E2 (PGE2) (in vitro) (PubMed:12804604, PubMed:17585783, PubMed:18198127). The biological function and the GSH- dependent property of PTGES2 is still under debate (PubMed:17585783, PubMed:18198127). In vivo, PTGES2 could form a complex with GSH and heme and would not participate in PGE2 synthesis but would catalyze the degradation of prostaglandin E2 H2 (PGH2) to 12(S)-hydroxy- 5(Z),8(E),10(E)-heptadecatrienoic acid (HHT) and malondialdehyde (MDA) (By similarity) (PubMed:17585783). {ECO:0000250|UniProtKB:Q9N0A4, ECO:0000269|PubMed:12804604, ECO:0000269|PubMed:17585783, ECO:0000269|PubMed:18198127}. This is the function of Ensembl gene identifier ENSG00000148334 (PTGES2, prostaglandin E synthase 2).