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First published online July 9, 2008; 10.1104/pp.108.122846 Plant Physiology 148:65-76 (2008) © 2008 American Society of Plant Biologists Two Arabidopsis ADP-Glucose Pyrophosphorylase Large Subunits (APL1 and APL2) Are Catalytic1Instituto de Bioquímica Vegetal y Fotosíntesis, Centro de Investigaciones Científicas Isla de la Cartuja, Universidad de Sevilla-CSIC, 41092–Sevilla, Spain (T.V., M.T.R., M.R.-P., F.V., J.M.R.); Department of Chemistry, Loyola University Chicago, Chicago, Illinois 60626 (M.L.K., M.A.B.); and Department of Biochemistry, Michigan State University, East Lansing, Michigan 48824 (J.P.)
ADP-glucose (Glc) pyrophosphorylase (ADP-Glc PPase) catalyzes the first committed step in starch biosynthesis. Higher plant ADP-Glc PPase is a heterotetramer (
1 This work was supported by the Ministerio de Educación y Ciencia (Spain; grant no. BIO2005–04916), by Junta de Andalucía (project no. P06–CVI–01450 and group CVI–281), and by the National Science Foundation (grant no. MCB0615982). Partial funding was provided by the Department of Energy (grant no. DE–FG02–93ER20121 to J.P.) and by the United States-Israel Binational Agricultural Research and Development Fund (research grant no. IS–3733–OSR to J.P.). M.R.-P. was supported by a fellowship from Fundacao para la Ciencia e a Tecnologia (Portugal), T.V. by an FPU fellowship, F.V. by a Ramón y Cajal contract from the Ministerio de Educación y Ciencia (Spain), and M.T.R. by an Averroes contract from Junta de Andalucía (Spain). The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: José M. Romero (jmromero{at}ibvf.csic.es). www.plantphysiol.org/cgi/doi/10.1104/pp.108.122846 * Corresponding author; e-mail jmromero{at}ibvf.csic.es. Received May 12, 2008; accepted June 30, 2008; published July 9, 2008. This article has been cited by other articles:
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2β2) consisting of two small and two large subunits. There is increasing evidence that suggests that catalytic and regulatory properties of the enzyme from higher plants result from the synergy of both types of subunits. In Arabidopsis (Arabidopsis thaliana), two genes encode small subunits (APS1 and APS2) and four large subunits (APL1–APL4). Here, we show that in Arabidopsis, APL1 and APL2, besides their regulatory role, have catalytic activity. Heterotetramers formed by combinations of a noncatalytic APS1 and the four large subunits showed that APL1 and APL2 exhibited ADP-Glc PPase activity with distinctive sensitivities to the allosteric activator (3-phosphoglycerate). Mutation of the Glc-1-P binding site of Arabidopsis and potato (Solanum tuberosum) isoforms confirmed these observations. To determine the relevance of these activities in planta, a T-DNA mutant of APS1 (aps1) was characterized. aps1 is starchless, lacks ADP-Glc PPase activity, APS1 mRNA, and APS1 protein, and is late flowering in long days. Transgenic lines of the aps1 mutant, expressing an inactivated form of APS1, recovered the wild-type phenotype, indicating that APL1 and APL2 have catalytic activity and may contribute to ADP-Glc synthesis in planta. 
