This protein plays a role in synthesis of starch. It catalyzes the synthesis of the activated glycosyl donor, ADP-glucose from Glc-1-P and ATP. alpha-D-glucose 1-phosphate + ATP + H(+) = ADP-alpha-D-glucose + diphosphate Activated by 3'phosphoglycerate, inhibited by orthophosphate. Allosteric regulation. Glycan biosynthesis; starch biosynthesis. Heterotetramer. Found in the chloroplast in leaf. Found in the plastid in the developing endosperm. Leaves and tubers. The strongest expression is seen in very small leaves (less than 1 cm in length) and decreases steadily as leaves become older. There is approximately 4- to 6-fold stronger expression in sink leaves relative to source leaves. Only minor variations in expression are seen during early stages of tuber development, however expression declines with increase in tuber size. By sucrose. Belongs to the bacterial/plant glucose-1-phosphate adenylyltransferase family.