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No evidence for the occurrence of substrate inhibition of Arabidopsis thaliana sucrose synthase-1 (AtSUS1) by fructose and UDP-glucose

AuthorsAlmagro, Goizeder ; Baroja-Fernández, Edurne ; Muñoz Pérez, Francisco José ; Bahaji, Abdellatif ; Etxebarría, E.; Li, Jun ; Montero, Manuel ; Hidalgo, Maite ; Sesma, María Teresa ; Pozueta Romero, Javier
Issue Date2012
PublisherLandes Bioscience
CitationPlant Signaling and Behavior 7(7): 799-802 (2012)
AbstractSucrose synthase (SuSy) catalyzes the reversible conversion of sucrose and NDP into the corresponding nucleotidesugars and fructose. The Arabidopsis genome possesses six SUS genes (AtSUS1-6) that code for proteins with SuSy activity. As a first step to investigate optimum fructose and UDP-glucose (UDPG) concentrations necessary to measure maximum sucrose-producing SuSy activity in crude extracts of Arabidopsis, in this work we performed kinetic analyses of recombinant AtSUS1 in two steps: (1) SuSy reaction at pH 7.5, and (2) chromatographic measurement of sucrose produced in step 1. These analyses revealed a typical Michaelis-Menten behavior with respect to both UDPG and fructose, with Km values of 50 μM and 25 μM, respectively. Unlike earlier studies showing the occurrence of substrate inhibition of UDP-producing AtSUS1 by fructose and UDP-glucose, these analyses also revealed no substrate inhibition of AtSUS1 at any UDPG and fructose concentration. By including 200 μM fructose and 1 μM UDPG in the SuSy reaction assay mixture, we found that sucrose-producing SuSy activity in leaves and stems of Arabidopsis were exceedingly higher than previously reported activities. Furthermore, we found that SuSy activities in organs of the sus1/sus2/sus3/sus4 mutant were ca. 80-90% of those found in WT plants. © 2012 Landes Bioscience.
Identifiersdoi: 10.4161/psb.20601
issn: 1559-2316
Appears in Collections:(IDAB) Artículos
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