Secretion of Proteins and Glycoproteins by the Rat Epididymis: Regional Differences, Androgen-Dependence, and Effects of Protease Inhibitors, Procaine, and Tunicamycin

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Abstract
Protein synthesis and secretion by the epididymis was studied in vitro by incubating tissue pieces with radioactive amino acids or one of a variety of radioactive sugars. When amino acids were used as precursors, about 15% of the incorporated radioactivity was released into the medium; the release was 36-65% in the case of sugar precursors. In different regions of the epididymis, pronounced variations were apparent in the profile of secreted proteins formed from amino acids or from galactose, mannose, or fucose. Total protein synthesis as measured by [35S) methionine incorporation was decreased by ∼30% following castration of animals, and the proportion of incorporated radioactivity which was secreted was reduced from 15% to 10%. Only a few qualitative changes were evident in the types of protein secreted. Compared with general protein synthesis, the incorporation of sugars into glycoproteins was affected by castration to a much greater extent, with mannose incorporation being reduced by up to 90% in the cauda. Protease inhibitors (TLCK, TPCK, PMSF, benzamidine, phenanthroline) reduced total protein synthesis from [35S] methionine but did not alter the profile of secreted proteins. Procaine also reduced total protein synthesis, and in the caput, but not the cauda, it caused a marked change in the pattern of secreted proteins. This differential effect of procaine did not appear to be due to an effect on "signal peptidase." Tunicamycin had little effect on protein synthesis and secretion by the epididymis when [35S] methionine was used as the precursor, although it did cause pronounced changes in protein secretion by testicular tissue. Greater effects of tunicamycin were evident when radioactive sugars were used as precursors, particularly in the case of [3H] mannose. The incorporation of this precursor was reduced to 69% and 49% of normal in the caput and cauda, respectively. However, tunicamycin did not alter the profile of secreted radioactive proteins resulting from any of the incubations with radioactive sugars.
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