Isolation of a Protease-producing Strain from Nong-xiang Daqu and Study on the Enzymatic Properties of the Produced Protease

A protease-producing strain was isolated successfully from Nong-xiang Daqu. Protease produced by such strain was treated by fractional precipitation, dialysis and resin to obtain the crude protease. Then the best pH value of the crude protease, its pH stability, its best temperature,its thermal stability, and the effects of metal ions on the crude protease were investigated. The results showed that, the optimum pH was 7 for such strain to produce protease and the pH stability of protease was poor; the optimum temperature for such strain to produce protease was at 40 ℃,and the thermal stability of protease decreased with the rise of temperature; Li+and EDTA chelating agent had inhibitory effects on the protease,however, Mn2+,Fe3+,Cu2+,K+,Zn2+,Mg2+and Ca2+could activate the protease, among them, Zn2+had the strongest activation effects on the protease.