ADPGlc

Table 4.1 Kinetic constants from ADPGlc PPases from higher plants, green algae, and cyanobacteria...

In the case of potato tuber ADPGlc PPase, the large subunit greatly increases the affinity of the small (catalytic) subunit for 3 PGA and lowers its affinity for the inhibitor, pi.55 56 in a plant, there may be only one conserved small (catalytic) subunit and several large (regulatory) subunits that can be distributed in different parts of the plant.83,87 This is of physiological importance, as expression of different large subunits... 

Table 4.2 Kinetic parameters for the 3PGA of A. thaliana recombinant ADPGlc PPase determined in the pyrophosphorolysis directiona,b...

Crystal Structure of Potato Tuber ADPGlc PPase... 

The crystal structure of the potato tuber homotetrameric small (catalytic) subunit ADPGlc PPase has been determined to 2.1 A resolution.64 The structures of the... 

Figure 4.2 Crystal structure of potato tuber ADP-glucose small (catalytic) subunit monomer. The catalytic domain is in yellow and the beta-helix domain is in pink. ADPGlc is shown in atom type carbon atoms are green, oxygen atoms are red, nitrogen atoms are blue, phosphorus atoms are magenta, and the sulfate group is orange. (The full color version ofthis figure can be found atwww.Elsevier.books.com/)...

Ghosh and Preiss65 were the first to show that the reaction catalyzed by ADPGlc PPase is activated by 3PGA and inhibited by Pi, and is an important step for regulation... 

Differences in Interaction Between 3PGA and Pi in Different ADPGlc PPases... 

Characterization of ADPGlc PPases from Different Sources... 

As previously indicated, Table 4.1 summarizes the kinetic and regulatory properties of various ADPGlc PPases, either partially purified away from interfering reactions or purified to homogeneity. Below is a summary of the properties of ADPGlc PPases from algae, leaf and plant reserve tissue. 

The ADPGlc PPase from potato tuber behaves similarly to the enzyme from plant leaves. It has been purified to apparent homogeneity (56.9U/mg), and it was the first plant heteromeric enzyme to be expressed fully active in E. coli.52>53,55,56 Immunolocalization of the ADPGlc PPase in developing potato tuber cells has shown that the enzyme is localized in the amyloplast.127... 

The barley leaf ADPGlc PPase has been purified to homogeneity (69.3 U/mg), and it shows high sensitivity toward activation by 3PGA and inhibition by Pi.75 Substrate kinetics and product inhibition studies in the synthesis direction suggested a sequential... 

Iso Ordered Bi Bi kinetic mechanism.75 ATP or ADPGlc bind first to the enzyme in the synthesis or pyrophosphorolysis direction, respectively, similar to the E. coli enzyme.89... 

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