Sugar isomerase that catalyzes the reversible isomerization of D-lyxose to D-xylulose, and D-mannose to D-fructose (PubMed:20695994). Shows optimum activity using D-lyxose as substrate, but can also effectively catalyze the isomerization between D-fructose and D-mannose (PubMed:20695994). Shows lower activity with L-gulose, D-talose and L-ribose (PubMed:20695994). D-lyxose = D-xylulose D-mannose = D-fructose kcat is 30810 sec(-1) with D-lyxose as substrate. kcat is 16170 sec(-1) with D-mannose as substrate. kcat is 31620 sec(-1) with D-xylulose as substrate. kcat is 4297 sec(-1) with D-fructose as substrate. Optimum pH is 7.5. Optimum temperature is 40 degrees Celsius. Homodimer. Belongs to the D-lyxose ketol-isomerase family.