3-Phosphoglycerate phosphatase in plants. I. Isolation and characterization from sugarcane leaves.

3-Phosphoglycerate phosphatase from sugarcane leaves (Saccharum) was purified 2530-fold to a specific activity of 740. The molecular weight was estimated to be about 160,000 by sucrose density gradient centrifugation. During electrophoresis with sodium dodecyl sulfate the protein divided into three or four subunits. The phosphatase was unstable above pH 7.5 but very stable from pH 4.5 to 6.5 at 4’ or -18’. Optimal activity of the purified enzyme was at pH 5.9; the isoelectric point was at pH 6.5 to 6.8. The enzyme specificity was not absolute; however, 3-phosphoglycerate was the preferred substrate. The Michaelis constant for d-phosphoglycerate was 2.8 X 10e4 M, and it was hydrolyzed stoichiometrically to glycerate and inorganic phosphate. No cofactors were required for activity, and the enzyme was stable in 1 mM ethylenediaminetetraacetate and other metal-complexing agents. The phosphatase was inhibited by 1 mM Zn++ and Cu++. Fluoride, L-( +)-tartrate, and molybdate gave typical phosphatase inhibition at 1 mM Glycidol phosphate was not hydrolyzed by the phosphatase, but inhibited the enzyme irreversibly and competitively. Three phosphonic acid derivatives were slightly stimulatory and were not hydrolyzed by the enzyme.