Abstract: In this study,the isolation and purification process of cell-envelope proteinase (CEP) from Lactococcus lactis subsp. lactis is determined as follows: suspending the washed Lactococcus lactis subsp. lactis cells by 50 mmol/L Tris-HCl (pH7.8) in lysis buffer solutio(n50 mmol/L Tris-HCl,2 mmol/L EDTA,100 mmol/L NaCl,0.5% Tritonx-100 and 1 mg/ml lysozyme,pH 8.5)at the ratio of 1:20 (g/ml)and then incubating the suspension for 3 h at 37 ℃,centrifugating the suspension and then collecting the supernatant (crude cell-envelope proteinase solution),fractionally precipitating the cell wall proteinase by adding 25%,45% and 65% ammonium sulfate into the supernatant,and purifying the crude proteinase by DEAE-Sephadex A-25 and Sephacryl-S-300 HR column chromatography successively. The enzyme is purified by about 74 folds from the crude cell-envelope proteinase solution and the the recovery of activity is about 14.87%. The purified enzyme showes a single protein band on native PAGE pattern,and it has a monomer structure and the molecular mass of about 53 kD by SAS-PAGE. The angiotensi converting enzyme (ACE) inhibitory rate of whey protein hydrolyzate by the purified enzyme is 45%.

Key words: ACE inhibitory activity, Lactococcus lactis subsp. lactis, cell wall proteinase