title: Activation of the potato tuber ADP-glucose pyrophosphorylase by thioredoxin.
abstract: The potato tuber (Solanum tuberosum L.) ADP-glucose pyrophosphorylase (ADP-GlcPPase) catalyzes the first committed step in starch biosynthesis. The main type of regulation of this enzyme is allosteric, and its activity is controlled by the ratio of activator, 3-phosphoglycerate to inhibitor, P(i). It was reported (Fu, Y., Ballicora, M. A., Leykam, J. F., and Preiss, J. (1998) J. Biol. Chem. 273, 25045-25052) that the enzyme was activated by reduction of the Cys(12) disulfide linkage present in the catalytic subunits. In this study, both reduced thioredoxin f and m from spinach (Spinacia oleracea) leaves reduced and activated the enzyme at low concentrations (10 microM) of activator (3-phosphoglycerate). Fifty percent activation was at 4.5 and 8.7 microM for reduced thioredoxin f and m, respectively, and 2 orders of magnitude lower than for dithiothreitol. The activation was reversed by oxidized thioredoxin. Cys(12) is conserved in the ADP-GlcPPases from plant leaves and other tissues except for the monocot endosperm enzymes. We postulate that in photosynthetic tissues, reduction could play a role in the fine regulation of the ADP-GlcPPase mediated by the ferredoxin-thioredoxin system. This is the first time that a covalent mechanism of regulation is postulated in the synthesis of starch.
authors.affiliation: Department of Biochemistry, Michigan State University, East Lansing, Michigan 48824, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Ballicora
authors.forename: J B
authors.initials: JB
authors.lastname: Frueauf
authors.forename: Y
authors.initials: Y
authors.lastname: Fu
authors.forename: P
authors.initials: P
authors.lastname: Schürmann
authors.forename: J
authors.initials: J
authors.lastname: Preiss
mesh_terms: D000494:Allosteric Regulation; D004229:Dithiothreitol / Q000494:pharmacology; D004789:Enzyme Activation; D051599:Glucose-1-Phosphate Adenylyltransferase; D005988:Glyceric Acids / Q000378:metabolism; D007700:Kinetics; D008956:Models, Chemical; D009713:Nucleotidyltransferases / Q000378:metabolism*; D010084:Oxidation-Reduction; D010710:Phosphates / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology; D011198:Solanum tuberosum / Q000201:enzymology*; D013879:Thioredoxins / Q000378:metabolism*
chemical_list: D005988:Glyceric Acids; D010710:Phosphates; D013879:Thioredoxins; C005156:3-phosphoglycerate; D009713:Nucleotidyltransferases; D051599:Glucose-1-Phosphate Adenylyltransferase; D004229:Dithiothreitol