Biochemical and thermodynamic characteristics of a new serine protease from URM 4133.

A protease from the fungus URM 4133, capable of producing bioactive peptides from goat casein, was purified. SDS-PAGE and zymography showed a molecular mass of 30 kDa. The enzyme was active and stable in a wide pH range (6.0-10.5) and (5.0-10.5), respectively. Optimum temperature was at 45-50 °C and stability was above 80 % (40 °C/2 h). Activity was not influenced by ions or organic substances (Triton, Tween, SDS and DMSO), but was completely inhibited by PMSF, suggesting that it belongs to the serine protease family. The Km and Vmax were 2.35 mg azocasein.mL-1 and 333.33 U.mg protein-1, respectively. Thermodynamic parameters of irreversible denaturation (40-60 °C) were enthalpy 123.63 - 123.46 kJ.mol-1, entropy 120.24-122.28 kJ.mol-1 and Gibbs free energy 85.97 - 82.45 kJ.mol-1. Any peptide sequences compatible with this protease were found after analysis by MALDI-TOF, which suggests that it is a new serine protease.