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Regulatory Properties of the ADP-Glucose Pyrophosphorylase of the Blue-Green Bacterium Synechococcus 6301 ¹

^a Department of Biochemistry and Biophysics, University of California, Davis, California 95616

ADP-glucose was found to be the primary sugar nucleotide used for glycogen synthesis by Synechococcus 6301. ADP-glucose pyrophosphorylase was partially purified 12-fold from this blue-green bacterium. The enzyme was activated 8- to 25-fold by glycerate 3-phosphate. Fructose 6-phosphate, fructose 1,6-bisphosphate, 5'-adenylate, and adenosine diphosphate activated the enzyme, but less than glycerate 3-phosphate. The enzyme was inhibited by inorganic phosphate. The I_0.5 of phosphate was 0.072 mM, and in the presence of 2 mM glycerate 3-phosphate, increased to 1.8 mM. The substrate saturation curves for glucose 1-phosphate and ATP were hyperbolic in both the presence and absence of glycerate 3-phosphate or phosphate. The saturation curve for MgCl₂ was sigmoidal; 2 mM glycerate 3-phosphate decreased the sigmoidicity from a Hill slope n value of 5.6 to 2.8, and increased the MgCl₂ optimum from 3 mM to 6 to 7 mM.