ADP-glucose

This enzyme [EC Unil], also known as ADP-glucose synthase and ADP-glucose pyrophosphorylase, catalyzes the reaction of a-o-glucose 1-phosphate with ATP to produce ADP-glucose and pyrophosphate. 

In vivo linear a-l,4-glucans are synthesized from ADP-glucose by the enzyme glycogen synthase [94-97]. The enzyme, as well as the monomer, are quite sensitive and therefore most researchers (at least in the field of polymer science) prefer to use phosphorylase for the synthesis of amylose. 

In Eq. (3) the hexokinase reaction ATP + glucose = ADP + glucose-6-phosphate with a standard free energy of AG b = -14.5 kJ/mol is introduced. AGb, standard free energy for ATP hydrolysis. 

ADP-Glucose Is the Substrate for Starch Synthesis in Plant Plastids and for Glycogen Synthesis in Bacteria... 

The mechanism of glucose activation in starch synthesis is similar to that in glycogen synthesis. An activated nucleotide sugar, in this case ADP-glucose, is... 

Starch synthesis is regulated at the level of ADP-glucose formation, as discussed below. 

Each of the two reactive groups (Xa, Xb) at the active site of starch synthase makes a nucleophilic attack on ADP-glucose, displacing ADP and forming a covalent attachment to C-l of the glucose unit. 

The hydroxyl at C-4 of glucose 3 displaces Xb from the disaccharide, forming a trisaccharide attached to Xa. Xb, now free, acquires glucose residue 4 from another ADP-glucose. 

FIGURE 20-28 Regulation of ADP-glucose phosphorylase by 3-phosphoglycerate and Pj. This enzyme, which produces the precursor for starch synthesis, is rate-limiting in starch production. The enzyme is stimulated allosterically by 3-phosphoglycerate (3-PGA) and inhibited by P, in effect, the ratio [3-PGA]/[Pi], which rises with increasing rates of photosynthesis, controls starch synthesis at this step. 

Starch synthase in chloroplasts and amyloplasts catalyzes the addition of single glucose residues, donated by ADP-glucose, to the reducing end of a starch molecule by a two-step insertion mechanism. Branches in amylopectin are introduced by a second enzyme. 

Review of the role of ADP-glucose pyrophosphorylase in the synthesis of amylose and amylopectin in starch granules. 

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