RESUMO
AIMS: Characterization of substrate specificity of a D-lyxose isomerase from Serratia proteamaculans and application of the enzyme in the production of D-lyxose and D-mannose. METHODS AND RESULTS: The concentrations of monosaccharides were determined using a Bio-LC system. The activity of the recombinant protein from Ser. proteamaculans was the highest for D-lyxose among aldoses, indicating that it is a D-lyxose isomerase. The native recombinant enzyme existed as a 54-kDa dimer, and the maximal activity for D-lyxose isomerization was observed at pH 7.5 and 40 degrees C in the presence of 1 mmol l(-1) Mn(2+). The K(m) values for D-lyxose, D-mannose, D-xylulose, and D-fructose were 13.3, 32.2, 3.83, and 19.4 mmol l(-1), respectively. In 2 ml of reaction volume at pH 7.5 and 35 degrees C, D-lyxose was produced at 35% (w/v) from 50% (w/v) D-xylulose by the D-lyxose isomerase in 3 h, while D-mannose were produced at 10% (w/v) from 50% (w/v) D-fructose in 5 h. CONCLUSIONS: We identified the putative sugar isomerase from Ser. proteamaculans as a D-lyxose isomerase. The enzyme exhibited isomerization activity for aldose substrates with the C2 and C3 hydroxyl groups in the left-hand configuration. High production rates of d-lyxose and d-mannose by the enzyme were obtained. SIGNIFICANCE AND IMPACT OF THE STUDY: A new D-lyxose isomerase was found, and this enzyme had higher activity for D-lyxose and D-mannose than previously reported enzymes. Thus, the enzyme can be applied in industrial production of D-lyxose and D-mannose.
