Abstract: Extracellular acid protease was obtained from Monascus anka CICC 40806 by ammonium sulfate precipitation, followed by anion exchange column chromatography with CM Sepharose, and then enzymatic and kinetic properties were determined. The results showed that the optimal pH value for the enzyme activity was 3.0 and the enzyme was stable in the pH range of 3.0–7.0. Its optimal reaction temperature was 50 ℃ and the enzyme was stable at temperature below 50 ℃; the attenuation constant at 50 ℃ was 0.569. The activation energy (Ea) was 28.85?kJ/mol when the substrate was casein. The protease had good salt resistance, and its residual enzymatic activity was 12% at a salt concentration of 7%. When the substrates were casein, rice dreg protein (RDP) and bovine serum albumin, the Km values were 12.48, 14.77 and 20.05?mg/mL, respectively, and it had higher catalytic efficiency for RDP and casein. The extracellular acid protease could play a positive role in fermentation and degradation of RDP.

Key words: Monascus anka, acid protease, purification, properties, kinetics