Partial characterization and activities of proteases from the digestive tract of discus fish ( Symphysodon aequifasciata)

A series of studies based on biochemical assays and electrophoretical observations was conducted in order to partially characterise various types of proteases present in the digestive tract of discus ( Symphysodon aequifasciata), a highly valuable ornamental species. Casein digestion assays revealed the presence of acidic protease from the stomach region with optimum activity at pH 2.0 and alkaline proteases from the intestinal section with optimum activities observed at pH ranging from 7.5 to 9.0 and 11.5 to 12.5, respectively. Further assays with specific substrates and also pre-incubation with specific protease inhibitors showed the importance of trypsin and chymotrypsin in protein digestion while also revealing the presence of serine-proteases and metallo-proteases, respectively. SDS-PAGE technique using casein as substrate and specific protease inhibitors also showed the presence of eight distinct proteases based on molecular weights ranging from 19.2 to 76.5 kDa.