A recombinant d-lyxose isomerase from Providencia stuartii was immobilized on Duolite A568 beads which gave the highest conversion of d-fructose to d-mannose among the various immobilization beads evaluated. Maximum activities of both the free and immobilized enzymes for fructose isomerization were at pH 7.5 and 45A degrees C in the presence of 1 mM Mn2+. Enzyme half-lives were 14 and 30 h at 35A degrees C and 3.4 and 5.1 h at 45A degrees C, respectively. The immobilized enzyme in 300 g fructose/l (replaced hourly), produced 75 g mannose/l at 35A degrees C = 25% (w/w) yield with a productivity of 75 g mannose l(-1) h(-1) after 23 cycles.