Substrate specificity of a recombinant d-lyxose isomerase from Serratia proteamaculans that produces d-lyxose and d-mannose

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°C in the presence of 1 mmol l Mn. The K values for d-lyxose, d-mannose, d-xylulose, and d-fructose were 13·3, 32·2, 3·83, and 19·4 mmol l, respectively. In 2 ml of reaction volume at pH 7·5 and 35°C, d-lyxose was produced at 35% (wv) from 50% (wv) d-xylulose by the d-lyxose isomerase in 3 h, while d-mannose were produced at 10% (wv) from 50% (wv) 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. © 2010 The Society for Applied Microbiology.