Five hundred ml of a 120-h culture of S. koyangensis strainTN650 were centrifuged for 30 min at 10,000 × g to remove micro-bial cells. The supernatant containing extracellular protease wasused as the crude enzyme preparation and submitted to the fol-lowing purification steps. It was initially saturated up to 40%with solid (NH4)2SO4and then centrifuged at 10,000 × g for20 min. The obtained supernatant was saturated up to 60% withsolid (NH4)2SO4, re-centrifuged, resuspended in a minimal vol-ume of buffer A containing 10 mM NaCl (Buffer B), and dialyzedovernight against repeated changes of the same buffer. The sam-ple thus obtained was deposited on a Mono S Sepharose column(2.6 × 20 cm) previously equilibrated with 50 mM HEPES buffersupplemented with 3 mM CaCl2at pH 6. The proteins were elutedwith the same buffer containing an increasing concentration ofNaCl of 0–500 mM at a rate of 30 ml/h. Fractions of each peakwere collected manually and analyzed by measuring absorbanceat 280 nm and the proteolytic activity on casein. Pooled frac-tions containing protease activity were concentrated in centrifugalmicro-concentrators (Amicon Inc., Beverly, MA, USA) with 10-kDacut-off membranes and stored at −20◦C for further analysis.