title: The potato tuber, maize endosperm and a chimeric maize-potato ADP-glucose pyrophosphorylase exhibit fundamental differences in Pi inhibition.
abstract: ADP-glucose pyrophosphorylase (AGPase) is highly regulated by allosteric effectors acting both positively and negatively. Enzymes from various sources differ, however, in the mechanism of allosteric regulation. Here, we determined how the effector, inorganic phosphate (Pi), functions in the presence and absence of saturating amounts of the activator, 3-phosphoglyceric acid (3-PGA). This regulation was examined in the maize endosperm enzyme, the oxidized and reduced forms of the potato tuber enzyme as well as a small subunit chimeric AGPase (MP), which contains both maize endosperm and potato tuber sequences paired with a wild-type maize large subunit. These data, combined with our previous kinetic studies of these enzymes led to a model of Pi inhibition for the various enzymes. The Pi inhibition data suggest that while the maize enzyme contains a single effector site that binds both 3-PGA and Pi, the other enzymes exhibit more complex behavior and most likely have at least two separate interacting binding sites for Pi. The possible physiological implications of the differences in Pi inhibition distinguishing the maize endosperm and potato tuber AGPases are discussed.
authors.affiliation: Program in Plant Molecular and Cellular Biology and Horticultural Sciences, University of Florida, 1253 Fifield Hall, Gainesville, FL 32611, USA.
authors.forename: Susan K
authors.initials: SK
authors.lastname: Boehlein
authors.forename: Janine R
authors.initials: JR
authors.lastname: Shaw
authors.forename: Donald R
authors.initials: DR
authors.lastname: McCarty
authors.forename: Seon-Kap
authors.initials: SK
authors.lastname: Hwang
authors.forename: Jon D
authors.initials: JD
authors.lastname: Stewart
authors.forename: L Curtis
authors.initials: LC
authors.lastname: Hannah
mesh_terms: D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000737:chemistry; D004795:Enzyme Stability; D051599:Glucose-1-Phosphate Adenylyltransferase / Q000737:chemistry* / Q000145:classification*; D010710:Phosphates / Q000737:chemistry*; D035281:Plant Tubers / Q000201:enzymology*; D030821:Plants, Genetically Modified / Q000201:enzymology*; D011198:Solanum tuberosum / Q000201:enzymology* / Q000235:genetics; D003313:Zea mays / Q000201:enzymology*
chemical_list: D004791:Enzyme Inhibitors; D010710:Phosphates; D051599:Glucose-1-Phosphate Adenylyltransferase
keywords: ADP-glucose pyrophosphorylase; Allosteric regulation; Mechanism; Phosphate inhibition