Faculté des sciences

Activation of the Potato Tuber ADP-glucose Pyrophosphorylase by Thioredoxin

Ballicora, Miguel A. ; Frueauf, Jeremiah B. ; Fu, Yingbin ; Schürmann, Peter ; Preiss, Jack

In: The Journal of Biological Chemistry, 2000, vol. 275, no. 2, p. 1315-1320

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, Pi. It was reported (Fu, Y., Ballicora, M. A., Leykam, J. F., and Preiss, J. (1998)... Plus

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    Summary
    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, Pi. 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 Cys12 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 µM) of activator (3-phosphoglycerate). Fifty percent activation was at 4.5 and 8.7 µM for reduced thioredoxin f and m, respectively, and 2 orders of magnitude lower than for dithiothreitol. The activation was reversed by oxidized thioredoxin. Cys12 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.