Purification and biochemical characterization of a novel alkaline protease from Aspergillus niger. Use in Antioxidant peptides production

This work reports the production of a novel alkaline protease from the fungus Aspergillus niger. The protease was purified from the culture supernatant to homogeneity using ammonium sulfate precipitation, Sephadex G-150 gel filtration and DEAE-sepharose ion exchange chromatography with a 13.9-fold increase in specific activity. The molecular weight of the enzyme was estimated to be 32 kDa on SDS-PAGE. The optimum pH and temperature were respectively, 9.0 and 50 °C. The enzyme stability was investigated over broad range of pH, temperature. The protease maintained considerable activity at the range of 30–60 °C and pH 7–10. The purified Aspergillus niger Protease (Prot-Asp) was used for the production of bioactive peptides. Grey mullet by products were hydrolyzed with purified protease in order to obtain peptides with biological activities. Interestingly, the hydrolysate (GMH) revealed the presence of antioxidant peptides.