l-Ribulose 5-Phosphate 4-Epimerase from Aerobacter aerogenes

Abstract l-Ribulose 5-phosphate 4-epimerase from Aerobacter aerogenes was inactivated by treatment with EDTA and was reactivated to varying extents by the addition of divalent metal ions in the order: Mn++ g Co++ g Ni++ g Ca++ g Zn++ g Mg++. When optimal Mn++ was present, the homogeneous enzyme had a specific activity of 70 µmoles-1 min-1 mg of protein at 28° and pH 7.2. This value is about five times greater than that displayed by the crystalline enzyme as isolated and assayed in the absence of added metal ion. In other mechanistic studies, l-ribulose 5-phosphate 4-epimerase was found to be stable to treatment with sodium sulfite and arsenite in the presence of a thiol compound. It was also stable to sodium borohydride in the presence or absence of substrate. Further, a reaction of tetranitromethane with the enzyme-substrate complex could not be detected. Possible mechanisms for l-ribulose 5-phosphate 4-epimerase are discussed.