Involved in synthesis of starch. Catalyzes the synthesis of ADP-glucose, a molecule that serves as an activated glycosyl donor for alpha-1,4-glucan synthesis. The chloroplastic isoform 1 is essential for starch synthesis in leaf chloroplasts and the cytosolic isoform 2 for synthesis in seed endosperm. alpha-D-glucose 1-phosphate + ATP + H(+) = ADP-alpha-D-glucose + diphosphate Activated by 3'phosphoglycerate, inhibited by orthophosphate. Allosteric regulation. Inhibited by inorganic phosphate (Pi). Glycan biosynthesis; starch biosynthesis. Heterotetramer composed of two small and two large subunits. Found in the chloroplast in leaf. Found in the plastid in the developing endosperm. Expressed in leaves. Expressed in developing seeds from 1 to 15 days after flowering (DAF). Shrunken seed endosperm due to a strong reduction in starch synthesis. Belongs to the bacterial/plant glucose-1-phosphate adenylyltransferase family.