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A comparison of heat stabilities and various kinetic properties between the adenosine diphosphoglucose pyrophosphorylases isolated from endosperm and embryo tissues from starchy maize seeds indicates that the adenosine diphosphoglucose pyrophosphorylase associated with the embryo is distinct from the enzyme isolated from the endosperm. The embryo enzyme is more stable to incubation for 5 minutes at 60 C while the endosperm enzyme is labile to this treatment. Both enzymes are activated by glycerate-3-P. The embryo enzyme is more sensitive to inhibition by phosphate than is the endosperm enzyme. Glycerate-3-P, which reverses the inhibition of the endosperm enzyme by phosphate, has little effect on the phosphate inhibition of the embryo enzyme. Other kinetic studies distinguish the two enzymes.A recent report (5) indicated the presence of ADP-glucose pyrophosphorylase in the embryo and endosperm tissues of maize seeds harvested in the milky stage, 22 days after selfpollination. The ADP-glucose pyrophosphorylase activity present in the embryo tissue of starchy maize (DeKalb 805) was only 1% of the total activity in the seed. However, the activity present in the embryo tissue of shrunken-2 mutant maize seeds was about 16% of the total ADP-glucose pyrophosphorylase activity in the seed since there was a drastic decrease in enzyme activity (about 92%) in the endosperm when compared to starch maize endosperm. As activities in the mutant and normal embryo tissues were about the same it was postulated that the mutation in Sh22 affected only the enzyme activity present in the endosperm but not in the embryo (5). This report will show that the kinetic and heat sensitivity properties of the ADP-glucose pyrophosphorylase present in the embryo of starchy maize are quite different than those of the endosperm ADP-glucose pyrophosphorylase. The properties of the embryo ADP-glucose pyrophosphorylase from Sh2 seeds are found to be very similar to the properties of the starchy maize embryo enzyme. MATERIALS AND METHODSSeeds of starchy maize (variety DeKalb 805) and Sh2 were harvested in the milky stage, 22 days after self-pollination, and stored at -10 C until use. Methods of assaying ADP-glucose

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