Trout ovulatory proteins are partially responsible for the anti-proteolytic activity found in trout coelomic fluid

After ovulation in salmonids, the eggs are held in the peritoneal cavity and bathed in coelomic fluid. Using a chromogenic peptide substrate, the anti-protease activity of brook trout coelomic fluid was measured. Trypsin, chymotrypsin, and pancreatic elastase activities were significantly inhibited by coelomic fluid containing 5.0, 10.0, and 25.0 mu g of total protein, respectively. Using subtractive cDNA cloning, we have previously characterized a set of ovarian proteins called TOPs (trout ovulatory proteins) that are secreted into the coelomic fluid after ovulation. TOPs are most homologous to mammalian antileukoprotease, a heat- and acid-stable serine protease inhibitor. On the basis of this homology, we hypothesized that the anti-trypsin activity observed in the coelomic fluid was related to the presence of TOPs. In the present study, this hypothesis was supported by the acid- and heat-stability of the anti-trypsin activity present in coelomic fluid. Coelomic fluid could be heated to 50 degrees C or treated at a pH less than 5.2 without a significant decrease in the inhibitory activity. Further, coelomic fluid from which TOPs were immunoprecipitated had significantly less anti-trypsin activity than nonimmunoprecipitated controls. We propose that TOP proteins are uniquely produced by the ovary and secreted into the coelomic fluid to act as protease inhibitors following ovulation.