Neutral serine protease from Penicillium italicum. Purification, biochemical characterization, and use for antioxidative peptide preparation from Scorpaena notata muscle.

In the present study, purification and properties of an extracellular neutral serine protease from the fungus Penicillium italicum and its potential application as an antioxidant peptides producer are reported. The protease was purified to homogeneity using ammonium sulfate precipitation, Sephacryl S-200 gel filtration, diethylaminoethanol (DEAE)-Sepharose ion exchange chromatography, and TSK-HPLC gel filtration with a 10.2-fold increase in specific activity and 25.8 % recovery. The purified enzyme appeared as single protein band with a molecular mass of 24 kDa in sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The optimum pH and temperature for the proteolytic activity were pH 7.0 and 50 °C, respectively. The enzyme was stable in the pH range of 6.0-9.0. The protease was activated by divalent cations such as Ca(2+) and Mg(2+). Complete inhibition of the purified enzyme by phenylmethylsulfonyl fluoride confirmed that the protease was of serine-type. The purified enzyme revealed high stability and relatively broad specificity. Scorpaena notata muscle protein hydrolysates prepared using purified serine protease (protease from P. italicum (Prot-Pen)) showed good in vitro antioxidative activities. The antioxidant activities of Scorpaena muscle protein hydrolyzed by Prot-Pen (SMPH-PP) were evaluated using various antioxidant assays: 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, reducing power, ferrous chelating activity, and DNA nicking assay. SMPH-PP showed varying degrees of antioxidant activity and almost the same strongest protection against hydroxyl radical induced DNA breakage.