2.A.7.9.23
The triose-P:Pi antiporter, TPT or Ape2 of 410 aas and 10 TMSs. Transports inorganic phosphate, 3-phosphoglycerate (3-PGA), 2-phosphoglycerate (2PG) and phosphoenolpyruvate (PEP) as well as triose phosphates. Functions in the export of photoassimilates from chloroplasts during the day. In the light, triose phosphates are exported from the chloroplast stroma in counter exchange with inorganic phosphate (Pi), generated for sucrose biosynthesis in the cytosol. Involved in photosynthetic acclimation, a light response resulting in increased tolerance to high-intensity light (Knappe et al. 2003). The crylstal structures of TPT from Galdieria sulphuraria have been solved revealing the protein bound to two different substrates, 3-phosphoglycerate and inorganic phosphate, in occluded conformations.