Sugar isomerase that catalyzes the reversible isomerization of D-lyxose to D-xylulose (PubMed:17189362). Shows weak activity with D-mannose and L-ribose (PubMed:17189362). D-lyxose = D-xylulose Optimum pH is 6.5. Optimum temperature is 70 degrees Celsius. Homodimer. Belongs to the D-lyxose ketol-isomerase family.