OBJECTIVETo identify the specific protein in the epididymal luminal fluid that may play a role in sperm epididymal maturation or modification on the surface of spermatozoa.

METHODSWe compared the differential protein components in the lumen fluids from the caput and cauda segments of the epididymis of normal rats as well as from the cauda segment of experimental left varicocele (ELV) rats by SDS-PAGE or 2D-electrophoresis. The protein spots of interest were selected for MS identification, and the target proteins further characterized by immuno-blot assay.

RESULTSMS analysis showed that one of the most prominent proteins, M(r) 22 000, was identical to the phosphatidylethanolamine-binding protein (PBP), and it was further identified as PBP by immuno-blot assay.

CONCLUSIONPBPs were present in a variety of molecular forms in the epididymal luminal fluid, including the glycosylated form, and ELV markedly elevated the PBP level in the cauda luminal fluid of the rats. Thus, the association of this molecule with sperm surface modification remains an interest for future investigation.