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Control of Photosynthetic Sucrose Synthesis by Fructose 2,6-Bisphosphate ¹

V. Modulation of the Spinach Leaf Cytosolic Fructose 1,6-Bisphosphatase Activity in Vitro by Substrate, Products, pH, Magnesium, Fructose 2,6-Bisphosphate, Adenosine Monophosphate, and Dihydroxyacetone Phosphate

Institute für Biochemie der Pflanze, Unter Karspüle 2, 3400 Gottingen, Federal Republic of Germany

How fructose 2,6-bisphosphate and metabolic intermediates interact to regulate the activity of the cytosolic fructose 1,6-bisphosphatase in vitro has been investigated. Mg²⁺ is required as an activator. There is a wide pH optimum, especially at high Mg²⁺. The substrate dependence is not markedly pH dependent. High concentrations of Mg²⁺ and fructose 1,6-bisphosphate are inhibitory, especially at higher pH. Fructose 2,6-bisphosphate inhibits over a wide range of pH values. It acts by lowering the maximal activity and lowering the affinity for fructose 1,6-bisphosphate, for which sigmoidal saturation kinetics are induced, but the Mg²⁺ dependence is not markedly altered. On its own, adenosine monophosphate inhibits competitively to Mg²⁺ and noncompetitively to fructose 1,6-bisphosphate. In the presence of fructose 2,6-bisphosphate, adenosine monophosphate inhibits in a fructose 1,6-bisphosphate-dependent manner. In the presence of adenosine monophosphate, fructose 2,6-bisphosphate inhibits in Mg²⁺-dependent manner. Fructose 6-phosphate and phosphate both inhibit competitively to fructose 1,6-bisphosphate. Fructose 2,6-bisphosphate does not affect the inhibition by phosphate, but weakens inhibition by fructose 6-phosphate. Dihydroxyacetone phosphate and hydroxypyruvate inhibit noncompetitively to fructose 1,6-bisphosphate and to Mg²⁺, but both act as activators in the presence of fructose 2,6-bisphosphate by decreasing the S_0.5 for fructose 1,6-bisphosphate. A model is proposed to account for the interaction between these effectors.

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				R. Zhou and L. Cheng Biochemical Characterization of Cytosolic Fructose-1,6-bisphosphatase from Apple (Malus domestica) Leaves Plant Cell Physiol., July 15, 2004; 45(7): 879 - 886. [Abstract] [Full Text] [PDF]