Abstract: The purification process of cell envelope protease (CEP) from Lactobacillus fermentum was explored in this paper. Cells were suspended in 50 mmol/L Tris-HCl (pH 7.8) and subjected to ultrasonication (cell concentration of 0.06 g/mL, ultrasonic power of 330 W, ultrasonic treatment time of 3 s with intermission of 5 s, and repeated ultrasonic treatment number of 220). The supernatant was collected, precipitated with 60% saturated (NH4)2SO4 solution and separated by Sephacryl S-300 HR chromatography. The active protease was recovered from Native-PAGE gel. The ACE inhibitory rate of purified CEP was 50%. The molecular mass of purified CEP estimated by SDS-PAGE was approximately 32.5 kD. Maximum activity was reached at pH 8.0 and 41℃. The activity of CEP could be activated by Mg2+, Co2+ and Ca2+ and inhibited by Zn2+, Ni2+ and PMSF, suggesting that CEP belongs to serine protease. On the other hand, its activity could also be inhibited by EDTA, suggesting that CEP is a metallopeptidase.

Key words: Lactobacillus fermentum, cell envelope protease, purification, enzymatic properties