The function of GPX8 (glutathione peroxidase 8 (putative), ENSG00000164294) is as follows. Acts as an endoplasmic reticulum (ER) thiol peroxidase that maintains ER redox homeostasis and protects the cytosol from ER-derived H(2)O(2)(PubMed:24566470, PubMed:32719007). Functions in a redox relay with ERO1A, using ERO1A-generated H(2)O(2) to drive PDI oxidation, linking peroxide detoxification to productive disulfide formation (PubMed:21215271). Modulates endoplasmic reticulum Ca(2+) levels mainly through SERCA pump activity and partially by influencing passive Ca(2+) leakage (PubMed:28129698). {ECO:0000269|PubMed:21215271, ECO:0000269|PubMed:24566470, ECO:0000269|PubMed:28129698, ECO:0000269|PubMed:32719007}.