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Characterization of Adenosine Diphosphate Glucose Pyrophosphorylases from Developing Maize Seeds ^1,2,3

^a Department of Genetics, University of Wisconsin, Madison, Wisconsin 53706

Electrophoretic examination of 22-day-old, normal maize (Zea mays L.) endosperm extracts revealed two zones of adenosine diphosphate glucose pyrophosphorylase activity. The enzymes are identical in terms of Km for glucose 1-phosphate and the effect of 3-phosphoglyceric acid on apparent Km for glucose 1-phosphate. Both enzymatic activities increase with increasing doses of the functional alleles at the shrunken-2 and brittle-2 loci. Molecular weight differences between the two electrophoretic species were inferred from sucrose gradient centrifugation. It is suggested that the two bands of activity represent different aggregation states of the same enzyme because under different extraction conditions, only one enzyme is found. Molecular weight estimates of 237,000 and 253,000 were obtained for the smaller enzyme. It is suggested that this enzyme is an aggregate of several subunits. Comparison of the embryo and endosperm pyrophosphorylases showed the embryo activity to be more heat stable and probably independent of direct shrunken-2 or brittle-2 control.

¹ Research was supported by the College of Agricultural and Life Sciences and by National Institutes of Health Grant 15422.

² The investigations reported were included in the thesis submitted by L.C.H. to the Graduate School, University of Wisconsin, Madison in partial fulfillment of the Ph.D. degree.

³ Laboratory of Genetics Paper No. 1756.

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