Inhibition of fructokinase and sucrose synthase by cytosolic levels of fructose in young tomato fruit undergoing transient starch synthesis |
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Authors: | Arthur A. Schaffer Marina Petreikov |
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Affiliation: | Dept of Vegetable Crops, Volcani Center-ARO, 50250, Bet Dagan, Israel. |
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Abstract: | Immature tomato fruit are characterized by a transient period of starch accumulation. Sucrose synthase (EC 2.4,1.13) and fructokinase (EC 2.7,1.4) are two of the initial enzymes in the sucrose to starch synthetic pathway. Both enzymes in tomato fruit are significantly inhibited by fructose at concentrations physiological to young tomato fruit. Compartmental analysis of immature fruit pericarp indicates that fructose is not specifically compartmentalized in the vacuole and that physiological cytosolic concentrations of fructose in young tomato fruit are above 30 m M . Such physiological levels of fructose significantly inhibit sucrose synthase cleavage activity as well as the activity of a partially purified fructokinase. These data suggest a mechanism of a coordinated, in vivo regulation of tomato sucrose synthase and fructokinase activity, which may be potentially limiting to starch accumulation in young tomato fruit. |
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Keywords: | Carbohydrate metabolism enzyme inhibition fructokinase fructose Lycopersicon esculentum sucrose metabolism sucrose synthase tomato |
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