ERO1-like protein alpha, also known as EPO1L, is an essential oxidoreductase that oxidizes proteins and is required for the folding of immunoglobulins. EPO1L covalently binds with PDI (protein disulfide-isomerase) and together they produce disulfide bonds between proteins in the endoplasmic reticulum. EPO1L is stimulated by hypoxia, suggesting that it is regulated through the HIF (hypoxia inducible transcrip-tion factor) pathway. EPO1L is ubiquitously expressed at low levels but expressed at high levels in upper digestive tract and esophagus. Recombinant human EPO1L protein, fused to His-tag at N-terminus, was expressed in E.coli and purified by using conventional chromatography techniques.