Sugar isomerase that catalyzes the reversible isomerization of D-lyxose to D-xylulose, and D-mannose to D-fructose (Ref.2). Shows optimum activity using D-lyxose as substrate, but can also effectively catalyze the isomerization between D-fructose and D-mannose (Ref.2). D-lyxose = D-xylulose D-mannose = D-fructose Can also use Ni(2+), Co(2+) or Fe(2+), with lower efficiency. kcat is 3108 min(-1) with D-lyxose as substrate. kcat is 5686 min(-1) with D-mannose as substrate. kcat is 1030 min(-1) with D-fructose as substrate. Optimum pH is 6.5. Retains more than 50% of maximal activity from pH 5.0 to 8.0. Optimum temperature is 65 degrees Celsius. Highly thermostable at 80 degrees Celsius. Homodimer. Belongs to the D-lyxose ketol-isomerase family.