Some Properties of 3-Phosphoglycerate Phosphatase from Developing Rice Grain

Abstract

Some properties of 3-P-glycerate phosphatase from developing caryopsis of rice (Oryza sativa L. variety IR26) were studied. The enzyme was soluble and not bound to starch and concentrated mainly in the pericarp-aleurone layer; its maximum activity was at 12-14 days after flowering. Contents of 3-P-glycerate and chlorophyll were highest in the grain at 7-8 days after flowering when starch synthesis was at a maximum. The enzyme was purified about 100-fold by precipitation with 50-80% ammonium sulfate, followed by chromatography through Sephadex G-200 and CM-Sephadex C-50. The pH optimum was from 5.7-6 and no cation was required for activity. The purified preparation had an apparent Km of 2.85 mM and was inhibited by Cu2+, Hg2+, Zn2+, Fe3+, 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 MW 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 2 phosphatase bands with 3-P-glycerate as substrate.