English: Substrates of the triose phosphate/phosphate translocators (TPTs) and nucleoside triphosphate transporters (NTTs) of the apicoplast of Plasmodium falciparum (A), of the diatom plastids from Thalassiosira pseudonana and Phaedactylum tricornutum (B), and of the crytomonad plastid from Guillardia theta (C). Overview of the metabolite transport processes for the characterized transporters of the chromalveolates. The presence of four envelope membranes reflects their secondary endosymbiotic origin. The TPT of the apicoplast of P. falciparum has a broader substrate specificity compared to the green counterpart, accepting also PEP (A). Diatom plastids are not able to synthesize nucleotides and therefore they depend on the import of nucleotides from the cytosol. They possess NTTs which catalyze a uniport mode of transport as in the chlamydial intracellular parasites from where these transporters were acquired (B). The cryptomonads contain a less reduced secondary endosymbiont, still harboring a vestigial nucleus in the periplasmic compartment, the former algal cytoplasm, where the starch is synthesized. The day and night path of carbon metabolism are regulated by differential expression of TPT genes whose products localize in different envelopes (C). Abbreviations: (d)NTP, (deoxy)nucleotide triphosphate; G3P, glycerol 3-phosphate; PEP, phosphoenolpyruvate; PfiTPT, P. falciparum innermost envelope TPT; PfoTPT, P. falciparum outermost envelope TPT; 3-PGA, 3-phosphoglycerate; Pi, inorganic phosphate; TP, triose phosphate; UDP-Glc, UDP-glucose.