Characterization and identification of proteins secreted in the various regions of the adult boar epididymis.

The synthesis and secretion of proteins by the boar genital tract were studied in vitro by incubating epididymal tissues with [35S]methionine and cysteine. Characterization of the major neosynthesized proteins was performed electrophoretically by one- and two-dimensional PAGE analysis, and an epididymal protein cartography was established. Some of the proteins secreted were found to be unregionalized. Polarization studies of the secretions in the epididymal tubule were carried out by in vitro incubation of isolated tubules, and most of these unregionalized proteins were found not to be secreted in the epididymal lumen. Inside the epididymal lumen, protein secretion was highly regionalized, and electrophoresis analysis detected few proteins secreted at all points along the organ. A total of 146 epididymal proteins, covering 220 spots, were found to be secreted by the epididymis. The distal caput showed the highest number of spots, the lowest number of proteins secreted being found in the proximal caput and cauda. Most of the epididymal proteins analyzed are highly polymorphic in terms of both isoelectric point and molecular mass. The presence and importance of the different compounds in the various regions of the epididymis were established. Several distinct secretory regions of the epididymis can be determined by the presence of major characteristic proteins. The concentrations of a given protein in the fluids of various regions were not related to the respective secretion intensity of that protein. Identification of some major epididymal proteins was accomplished by N-terminal amino microsequencing and by the use of specific antisera. Of the various major proteins, clusterin, glutathione peroxidase, retinol-binding protein, lactoferrin, EP4, beta-N-acetyl-hexosaminidase, alpha-mannosidase, and procathepsin L were identified and localized along the organ. Several polypeptides found in this study remain unidentified.