Biochemical Properties of a Novel d-Mannose Isomerase from Pseudomonas syringae for d-Mannose Production

d-Mannose isomerase can reversibly catalyze d-fructose to d-mannose which has various beneficial effects. A novel d-mannose isomerase gene (PsMIaseA) from Pseudomonas syringae was cloned and expressed in Escherichia coli. The recombinant d-mannose isomerase (PsMIaseA) showed the highest amino acid sequence homogeneity of 50% with ManI from Thermobifda fusca. PsMIaseA was purified through Ni-NTA chromatography, and its specific activity was 818.6 U mg(-1). The optimal pH and temperature of PsMIaseA were pH 7.5 and 45 degrees C, respectively. The enzyme was stable within a wide pH range from 5.0 to 10.0. It could efficiently convert d-fructose to d-mannose without any metal ions. When PsMIaseA was incubated with 600 g/L d-fructose for 6 h, the space-time yield of d-mannose reached 27.2 g L-1 h(-1) with a maximum conversion ratio of 27%. Therefore, the d-mannose isomerase may be suitable for green production of d-mannose.