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Enzymatic Characteristics of Thermostable p-Nitrophenylphosphatase

Thermostable p-nitrophenylphosphatase (TNPPase) had been expressed in E. coli M15, and purified rapidly. It is sensitive to metal chelator and Mg ion is necessary to its activity. TNPPase exhibited a moderate degree of thermostability, and the thermostability of TNPPase increased significantly when treated with 1 mmol/L Mg, Mn, Cu, Ba, Ca, Ni and Zn ions. TNPPase is stable within a wide range of pH (pH 7.0～12.0). It catalyzed the hydrolysis of p-nitrophenylphosphate with a Michaelis constant 3.031 mmol/L and a V max 313.5 μmol·min -1 ·mg -1 . The α-helix percentage and β-turn percentages were 74.5 and 25.5 in the secondary structure of TNPPase, respectively. TNPPase is not stable in SDS solution, but stable in Triton X-100 and Tween 20 solutions.