Purification and properties of D-ribulose-5-phosphate 3-epimerase from calf liver.

D-Ribulose-5-phosphate 3-epimerase (EC 5.1.3.1) was purified 760-fold from calf liver by adsorption on DEAE-cellulose, chromatography on DEAE-Sephadex, chromatography on D-ribose 5-phosphate-Sepharose and gel filtration on Biogel P200. The purified enzyme of specific activity 617 units/mg was obtained in 28% yield and gave a single band on polyacrylamide gel electrophoresis. It had a molecular weight of 45 000 and appeared to contain two identical peptide chains of 22 900 daltons. The Km for D-ribulose 5-phosphate was 0.19 +/- 0.07 mM (S.E.). It was inhibited by reagents reacting with sulphydryl groups, by sulphate ion, and by D-deoxyribose 5-phosphate. The pH-stability and pH-activity curves were determined.