Substrate specificity of a recombinant D-lyxose isomerase from Providencia stuartii for monosaccharides(ENZYMOLOGY, PROTEIN ENGINEERING, AND ENZYME TECHNOLOGY)

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The specific activity and catalytic efficiency (k_<cat>/K_m) of the recombinant putative protein from Providencia stuartii was the highest for D-lyxose among the aldose substrates, indicating that it is a D-lyxose isomerase. Gel filtration analysis suggested that the native enzyme is a dimer with a molecular mass of 44kDa. The maximal activity for D-lyxose isomerization was observed at pH 7.5 and 45℃ in the presence of 1mM Mn^<2+>. The enzyme exhibited high isomerization activity for aldose substrates with the C2 and C3 hydroxyl groups in the left-hand configuration, such as D-lyxose, D-mannose, L-ribose, D-talose, and L-allose (listed in decreasing order of activity). The enzyme exhibited the highest activity for D-xylulose among all pentoses and hexoses. Thus, D-lyxose was produced at 288g/l from 500g/l D-xylulose by D-lyxose isomerase at pH 7.5 and 45℃ for 2h, with a conversion yield of 58% and a volumetric productivity of 144g l^<-1>h^<-1>. The observed k_<cat>/K_m (920mM^<-1>s^<-1>) of P. stuartii D-lyxose isomerase for D-xylulose is higher than any of the k_<cat>/K_m values previously reported for sugar and sugar phosphate isomerases with monosaccharide substrates. These results suggest that the enzyme will be useful as an industrial producer of D-lvxose.