Catalyzes the reversible interconversion of fructoselysine with its C-3 epimer, psicoselysine. Allows E.coli to utilize psicoselysine for growth. Does not act on psicose or fructoselysine 6-phosphate. N(6)-(D-psicosyl)-L-lysine = N(6)-(D-fructosyl)-L-lysine Can use Ni(2+) or Co(2+) in vitro, and, to a lesser extent, Fe(2+) or Mn(2+), but not Ca(2+) or Cu(2+). Homooctamer. Belongs to the FrlC family.