초록
The gene encoding a putative mannose-6-phosphate isomerase (TnMPI) from Thermotoga neapolitana DSM4359 was cloned and expressed in Escherichia coli.TnMPI showed the highest isomerization activity between D-fructose and D-mannose at 75oC in 50 mM Tris-HCl buffer (pH 7.5) containing 1 mM of Cu2+. TnMPI can be activated by some divalent metal ions, such as Cu2+, Mn2+,and Co2+. In the presence of 1 mM Cu2+, TnMPI activity on conversion from D-fructose to D-mannose was significantly enhanced up to 271% of that without Cu2+. In addition, its isomerization equilibrium between D-fructose and Dmannose was strongly affected by reaction temperature and pH. As reaction temperature decreased from 95 to 55oC,the equilibrium ratio of D-fructose to D-mannose was gradually shifted from 73:27 to 55:45. As reaction pH decreased from pH 8.5 to 5.5, the equilibrium ratio of Dfructose to D-mannose was shifted from 68:32 to 49:51.