Plant ADPGIc PPases can be Activated by Thioredoxin

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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