Pyrophosphorylases in Solanum tuberosum: I. Changes in ADP-Glucose and UDP-Glucose Pyrophosphorylase Activities Associated with Starch Biosynthesis during Tuberization, Maturation, and Storage of Potatoes.

Changes in ADP-glucose and UDP-glucose pyrophosphorylase activities were followed during tuber development of Solanum tuberosum and prolonged storage at 4 and 11 C. Potato tuberization was accompanied by a sharp increase in starch synthesis simultaneous with a marked rise in ADP-glucose pyrophosphorylase activity. When tubers reached an average diameter of 1 centimeter (0.5 gram average tuber weight) and had already established 58% starch on a dry weight basis, ADP-glucose pyrophosphorylase increased 16- to 24-fold over its activity seen in low starch containing stolon tissue. During this same period UDP-glucose pyrophosphorylase increased approximately 2- to 3-fold. Although participation of UDP-glucose in starch formation can not be neglected, it is suggested that the onset of rapid non-photosynthetic potato tuber starch biosynthesis may be closely related to the simultaneous increase in ADP-glucose pyrophosphorylase activity.Evidence that UDP-glucose and ADP-glucose pyrophosphorylases are separate protein entities was indicated by their (a) activity ratio variations during tuber development and storage, (b) extraction stabilities, (c) morphological localization, (d) separation with ammonium sulfate, (e) pH optima, and (f) differential activation with 3-P-glycerate.