Purification and properties of heat-stable extracellular protease from Pseudomonads fluorescens BJ-10

Pseudomonas fluorescens BJ-10, a kind of psychrotrophic bacteria, was isolated from raw milk. It produced an extracellular protease of 47 kDa by SDS-PAGE. The crude proteases were purified by ammonium sulfate fractionation, ion-exchange and gel filtration chromatography. The specific activity of purified protease increased 61.38-fold. The optimum pH and temperature were pH 7.0 and 30 °C, respectively. The purified protease was partially inhibited by DL-dithiothreitol, and the activity increased a little upon Fe(2+) addition. The protease showed typical heat-stable behavior. After treatment at 100 °C for 3 min, more than 94% activity remained. This work might lay the foundation for possible relationship between the heat stable protease and gelation of UHT milk.