Purification of human secretory pregnancy-associated endometrial alpha 2-globulin (alpha 2-PEG) from cytosol of first trimester pregnancy endometrium.

Pregnancy-associated endometrial alpha 2-globulin (alpha 2-PEG), the major secretory protein as assessed by in-vitro synthesis and secretion by the endometrium during the luteal phase of the menstrual cycle and early first trimester of pregnancy, has been purified from the cytosolic fraction of pregnancy endometrium. The purification schedule involved anion exchange chromatography (DE52), gel filtration (Sephacryl S-200), concanavalin A-Sepharose, chromatofocusing and negative immunoaffinity chromatography. On anion exchange chromatography alpha 2-PEG eluted at 0.11 M NaCl, on Sephacryl S-200 with an apparent Mr of 56 K, it bound to concanavalin A and eluted from a chromatofocusing column at a pH of 4.6. alpha 2-PEG was isolated with 98% purity, as assessed by one-dimensional sodium dodecyl sulphate (SDS)-gradient polyacrylamide gel electrophoresis (subunit Mr under reducing conditions 28 K), and a yield of 0.11 mg per g wet weight tissue. This purified alpha 2-PEG should enable in-vitro assessment of the function of this unique protein in implantation and pregnancy and provide antigenic material for the development of a radioimmunoassay.