The Purification and Properties of Guanosine Diphosphate Glucose Pyrophosphorylase of Pea Seedlings

400 fold purification of GDP glucose pyrophosphorylase from pea seedlings concomitant with stabilization of enzyme activity has been accomplished by (NH4)2SO4 fractionation, followed by chromatography on Sephadex G200 and DEAE‐celluose columns. In this last step the enzyme is eluted with 0.20 M NaCl. The enzyme is specifically activated by Mn2+. The apparent Km value for glucose‐1‐phosphate (37°, pH 7.5) is about 3 × 10−4 M. The GDP glucose'biosynthesis is found to be reversible, with the equilibrium in favour of pyrophosphorolysis. The purified enzyme is not active with GTP plus mannose‐1‐phosphate or galactose‐1‐phosphate. No formation of nucleotide sugar is observed in the presence of glucose‐1‐phosphate plus ATP, ITP, dTTP, or CTP. A small residual UDPG pyrophosphorylase activity is activated by Mg2+.