A putative D-lyxose isomerase from Dictyoglomus turgidum was purified with a specific activity of 19 U/mg for D-lyxose isomerization by heat treatment and affinity chromatography. The native enzyme was estimated as a 42 kDa dimer by gel-filtration chromatography. The activity of the enzyme was highest for D-lyxose, suggesting that it is a D-lyxose isomerase. The maximum activity of the enzyme was at pH 7.5 and 75°C in the presence of 0.5 mM Co(2+), with a half-life of 108 min, K(m) of 39 mM, and k(cat) of 3,570 1/min. The enzyme is the most thermostable D-lyxose isomerase among those characterized to date. It converted 500 g D-xylulose/l to 380 g D-lyxose/l after 2 h. This is the highest concentration and productivity of D-lyxose reported thus far.
