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-cellulose columns. In this last step the enzyme is eluted with 0.20 M NaCl. The enzyme is specifically activated by Mn²⁺. The apparent K_m 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⁺. [ABSTRACT FROM AUTHOR]