Characterization of the maturation-associated galactose oxidase-sensitive glycoproteins of rat caudal sperm plasma membrane and epididymal fluid

This paper explores the relationship between the galactose oxidase-sensitive glycoproteins from rat caudal epididymal sperm and fluid and, in addition, their relatedness to the 32,000-Da major acidic secretory glycoproteins of caudal epididymal fluid. The major acidic secretory glycoproteins were purified by a combination of high-resolution anion-exchange (Mono Q) and gel permeation (Bio-Sil TSK 125) chromatographic steps. Immunoprecipitation studies, peptide mapping, and the inability to label the purified glycoprotein by galactose oxidase/sodium boro[ 3H]hydride clearly established that the galactose oxidase-sensitive fluid and membrane glycoproteins were not related to these acidic secretory glycoproteins. Membrane and fluid tritium-labeled glycoproteins were shown to be closely related, but not identical, polypeptides. Sugar analysis indicated that both glycoproteins contain N- and O-linked saccharide chains and that the galactose oxidase-sensitive residue was present only on O-linked sugars. It was also found that efficient labeling of the 32,000-Da fluid glycoprotein was possible only if protease inhibitors were omitted from all buffers used in the isolation of caudal epididymal fluid and subsequent labeling procedures. This suggests that the fluid glycoprotein was acquired by the unintentional proteolysis of the membrane glycoprotein. Polyclonal antibodies raised against caput sperm plasma membranes immunoprecipitated tritium-labeled glycoproteins from both caudal epididymal fluid and sperm membrane, suggesting that a precursor form of the caudal galactose oxidase-sensitive glycoprotein may be present on caput sperm.