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Fig. 1 | BMC Plant Biology

Fig. 1

From: Mathematical kinetic modelling followed by in vitro and in vivo assays reveal the bifunctional rice GTPCHII/DHBPS enzymes and demonstrate the key roles of OsRibA proteins in the vitamin B2 pathway

Fig. 1

Riboflavin biosynthetic pathway. The riboflavin pathway starts with the hydrolytic release of formate and inorganic pyrophosphate from (1) GTP catalyzed by GTP cyclohydrolase II (GTPCHII) giving rise to the pyrimidine derivative: (2) 2,5-diamin-6-ribosylamino-4(3H)-pyrimidinone 5’-phosphate [32] (DA6RP5P). This product is converted into (4) 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione 5’-phosphate (ARPP) via (3) 5-amino-6-ribosylamino-2,4(1H, 3H)-pyrimidinedione 5'-phosphate (A6RP5P) reactions catalyzed by 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)pyrimidine deaminase (PYRD) and 5-amino-6-(5-phosphoribosylamino)uracil reductase (PYRR). ARPP is converted into ARP by a hypothetical phosphatase, not yet identified in plants [39]. The resulting pyrimidine derivative yields (8) 6,7-dimethyl-8-ribityllumazine (DMRYL) by condensation with (7) 3,4-dihydroxy-2-butanone 4-phosphate (DHB4P) catalyzed by lumazine synthase, (LS) which is obtained from (6) ribulose 5-phosphate (Rub5P) by a skeletal rearrangement (by the action of 3,4-dihydroxy-2-butanone 4-phosphate synthase (DHBPS)) [39]. The final step of the biosynthetic pathway yields (9) riboflavin and the pyrimidine catalyzed by riboflavin synthase (RS). Adapted from Fischer and Bacher (2006) [39]. Abbreviations: (1) GTP, guanosine-5'-triphosphate; (2) 2,5-diamin-6-ribosylamino-4(3H)-pyrimidinone 5’-phosphate (DA6RP5P); (3) 5-amino-6-ribosylamino-2,4(1H, 3H)-pyrimidinedione 5'-phosphate (A6RP5P); (4) 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione 5’-phosphate (ARPP); (5) 5-amino-6-ribitylamino-2,4 (1H,3H)-pyrimidinedione (ARP); (6) ribulose 5-phosphate (Rub5P); (7) 3,4-dihydroxy-2-butanone 4-phosphate (DHB4P); (8) 6,7-dimethyl-8-ribityllumazine (DMRYL); (9) riboflavin; (10) flavin mononucleotide (FMN); (12) flavin dinucleotide (FAD). HCOO−, formate; PPi, pyrophosphate; 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

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BMC Plant Biology

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