The enzymes isolated from the bacteria?Pseudomonas cichorii?[2],?Pseudomonas?sp. ST-24 [1],?Rhodobacter sphaeroides?[3] and?Mesorhizobium loti?[4] catalyse the epimerization of various ketoses at the C3?position, interconverting?D-fructose and?D-psicose,?D-tagatose and?D-sorbose,?D-ribulose and?D-xylulose, and?L-ribulose and?L-xylulose. The specificity depends on the species. The enzymes from?Pseudomonas cichorii?and?Rhodobacter sphaeroides?require Mn2+?[2,3].