Protein Disulfide Isomerase (PDI) is a multifunctional, ubiquitous enzyme. It has long been known to catalyze formation of native disulfides of peptide chains, thereby acting as a chaperone to assist in protein folding. EP52 is a novel 52kd protein isolated from rat epidermis with 90% homology in nucleotide sequence to the hamster P5 gene, a member of the PDI superfamily. It contains two copies of the thioredoxin (C-G-H-C) like sequence and is thus expected to exhibit PDI-like activity. We isolated total RNA from different tissues of two day old Sprague-Dawley rats and synthesized two primers, one containing the nucleotide sequence of N-terminus and the other the sequence that includes the second thioredoxin-like active site. Using RT-PCR, we observed amplification of the EP-52 mRNA in dermis, liver, kidney, and skeletal muscle, in addition to epidermis. Since the epidermal source is limited for activity detection, dermal tissue containing hair follicles was homogenized in 20mM Tris-HCl containing 1mM EDTA, 1mM DTT, and 0.43mM PMSF. The supernatant was collected after centrifugation and fractionated by Q-Sepharose column chromatography. Fractions eluted with 0.5 M NaCl linear gradient were tested for PDI activity using the renaturation of denatured ribonuclease AIII method of Rupp et al (J.B.C. 269,2501,1994). Fractions with activity contained a protein band, of Mr about 50kd as determined by SDS-PAGE, suggesting that the dermal homologue of EP52 is a protein that probably plays an important functional role in the physiology of that tissue.