Extraction and biochemical characterization of peptidases from giant catfish viscera by aqueous two-phase system

Peptidases were extracted from the viscera of farmed giant catfish (Pangasianodon gigas) in an aqueous two-phase system (ATPS) of 15% (w/w) polyethylene glycol (PEG-2000) and 15% (w/w) sodium citrate. The recovery of the enzymes was 273% with 12-fold purification. Protein pattern, activity and inhibitory staining confirmed that the proteins with molecular weights of 12 and 31kDa were a mixture of proteolytic enzyme. The optimum pH and temperature of the enzyme were 8.0 and 70C, respectively. Besides, it retained more than 50% of activity at the highest salt concentration (30% w/v). The enzyme was strongly inhibited by serine protease inhibitors (>80% inhibition), while low inhibition with cysteine-, aspartic- and metallo-protease inhibitors (<20% inhibition). The enzyme activity was extremely inhibited by the metal ions Ag+, Cu2+ and Fe2+. The peptidases from the giant catfish viscera have potential applications in food processing where high temperatures (60-70C) and/or high salt content are used, or even in detergent formulation. Practical Applications: Extraction and characterization of a proteolytic enzyme from viscera, fishery processing by-product, could add value to it. According to its properties, the isolated peptidases could be potentially applied to food industry, especially in fish sauce production, protein hydrolysate production, or in neutraceutical and in detergent industry.