Some properties of 3-phosphoglycerate phosphatase from developing rice grain

Some properties of 3-P-glycerate phosphatase from developing caryopsis of rice (Oryza sativa L., variety IR26) were studied. The enzyme was found to be soluble and not bound to starch, and concentrated mainly in the pericarp-aleurone layer; its maximum activity was at 12 to 14 days after flowering. Contents of 3-P-glycerate and chlorophyll were highest in the grain at 7 to 8 days after flowering when starch synthesis was at a maximum. The enzyme was purified about 100-fold by precipitation with 50 to 80% ammonium sulfate, followed by chromatography through Sephadex G-200 and CM-Sephadex C-50. The pH optimum was from 5.7 to 6 and no cation was required for activity. The purified preparation had an apparent Km of 2.85 mm and was inhibited by Cu(2+), Hg(2+), Zn(2+), Fe(3+), molybdate, and F(-). The enzyme also exhibited high activity toward UTP, ATP, and p-nitrophenyl phosphate; moderate activity toward other phosphates; but no activity toward phytate. A molecular weight of about 23,000 was obtained for the 3-P-glycerate peak during gel filtration on Sephadex G-200, which corresponded to a value of 26,000 for the major protein fraction by thin layer gel filtration on Sephadex G-150. Zymograms of the whole extract and semipurified preparations showed two phosphatase bands with 3-P-glycerate as substrate.