Purification and Localization of Acidic Epididymal Glycoprotein (AEG): A Sperm Coating Protein Secreted by the Rat Epididymis

A protein designated acidic epididymal glycoprotein (AEG) was purified from rat epididymis using ion exchange chromatography on DEAE-Sephadex, gel filtration in Sephadex G-75 and affinity chromatography on Concanavalin-A Sepharose. AEG is a major secretory product of the epididymis making up 2–3 per cent of total soluble protein. Antibody to AEG was raised in rabbits and purified by affinity chromatography on AEG-Sepharose. Quantitation of AEG in cytosol using "rocket" immunoelectrophoresis showed AEG to increase in epididymal segments from caput to cauda. Ligation of the midcorpus decreased AEG in the cauda. Localization of AEG using an immunoperoxidase method revealed that it is secreted largely by the epithelium of caput and corpus beginning with the region distal to the initial segment. It appears to be secreted by a specific cell type, probably the so-called "principal" cell. Specific staining of AEG was also noted in "clear" cells in the cauda. Spermatozoa become coated with AEG as they leave the initial segment and remain so during passage through the cauda.