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. Prominently expressed in the leaves. A lower level expression is seen in the roots. Belongs to the bacterial/plant glucose-1-phosphate adenylyltransferase family.