Fig. 2

Riboflavin biosynthesis pathway and kinetic model simulation results. A Simplified riboflavin biosynthesis. The bifunctional RibA (GTP cyclohydrolase II/ 3,4-dihydroxy-2-butanone 4-phosphate synthase) mediates the synthesis of (7) DHB4P and (2) DA6RP5P which is converted into (5) ARP by the serial action of PYRD, PYRR and a hypothetical phosphatase not yet identified in plants [39]. LS condensates (7) DHBPS and (5) ARP to yield (8) DMRYL, which is converted into (9) riboflavin by the action of RS [33]. The translocation of ARP into the plastid and the translocation of FAD into the cytosol are hypothesized, although no corresponding transporters have been identified in plants thus far [39]. B Simulation results for riboflavin production along time in the non-optimized model (Green, Normal conditions), overexpressing PYRD (pink), overexpressing PYRR (purple), overexpressing RS (gray) and overexpressing bifunctional RibA (dark red). Abbreviations: (1) GTP, guanosine-5'-triphosphate; (2) DA6RP5P, 2,5-diamin-6-ribosylamino-4(3H)-pyrimidinone 5’-phosphate; (3) A6RP5P, 5-amino-6-ribosylamino-2,4(1H, 3H)-pyrimidinedione 5'-phosphate; (4) ARPP, 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione 5’-phosphate; (5) ARP, 5-amino-6-ribitylamino-2,4 (1H,3H)-pyrimidinedione (ARP); (6) Rub5P, ribulose 5-phosphate; (7) DHB4P, 3,4-dihydroxy-2-butanone 4-phosphate; (8) DMRYL, 6,7-dimethyl-8-ribityllumazine; (9) riboflavin; (10) FMN, flavin mononucleotide; (12) FAD, flavin dinucleotide. Bifunctional RibA, GTP cyclohydrolase II/3,4-dihydroxy-2-butanone 4-phosphate synthase; PYRD, 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)pyrimidine deaminase; PYRR, 5-amino-6-(5-phosphoribosylamino)uracil reductase; LS, lumazine synthase; RS, riboflavin synthase; RK, riboflavin kinase; FADS, FAD synthetase