Biosynthesis of vitamin B₂ in plants

Abstract

The biosynthesis of one riboflavin (vitamin B2) molecule requires one molecule of GTP and two molecules of ribulose 5‐phosphate. The imidazole ring of GTP is hydrolytically opened, yielding a 2,5‐diaminopyrimidine that is converted to 5‐amino‐6‐ribitylamino‐2,4(1H,3H)‐pyrimidinedione by a sequence of deamination, side chain reduction and dephosphorylation. Condensation of 5‐amino‐6‐ribitylamino‐2,4(1H,3H)‐pyrimidinedione with 3,4‐dihydroxy‐2‐butanone 4‐phosphate obtained from ribulose 5‐phosphate yields 6,7‐dimethyl‐8‐ribityllumazine. Dismutation of the lumazine derivative yields riboflavin and 5‐amino‐6‐ribitylamino‐2,4(1H,3H)‐pyrimidinedione, which is recycled in the biosynthetic pathway. Characteristic architectural features of most enzymes involved in the plant riboflavin pathway resemble those of eubacteria, whereas the similarities between plants and yeasts are less pronounced. Moreover, riboflavin biosynthesis in plants proceeds by the same reaction steps as in eubacteria, whereas fungi use a somewhat different pathway.

Genetic Control of Biosynthesis and Transport of Riboflavin and Flavin Nucleotides and Construction of Robust Biotechnological Producers

“…The biochemical pathways of RF synthesis appeared to be similar, but not identical, in bacteria, fungi, and plants (see below). Surprisingly, the pathways of RF synthesis are identical in eubacteria and plants but different in fungi and archaea (112)(113)(114)(115). One important step in RF synthesis remains unknown, namely, the conversion of the phosphorylated pyrimidine derivative of RF to its nonphosphorylated derivative (the dephosphorylation step).…”

“…2). The sequence of deamination and reduction is distinct in fungi and archaea on the one hand and bacteria and plants on the other (14,112,113). In yeasts and fungi, the enzyme catalyzing the second reaction of RF biosynthesis, 2,5-diamino-6-ribosylamino-4(3H)-pyrimidinone 5-phosphate reductase [another name is 2,5-diamino-6-ribitylamino-4(3H)-pyrimidinone 5-phosphate synthase] (EC 1.1.…”

“…Comprehensive reviews of the biochemistry of RF synthesis have been published by Bacher and his colleagues (13,14,(112)(113)(114)(115). The following brief overview of the RF biosynthesis pathway is based on these reviews and recent publications.…”

Studies on organogenesis during regeneration in the earthworm, Eudrilus eugeniae, in support of symbiotic association with Bacillus endophyticus

“…It is known that the riboflavin is synthesized only by microbes (Prabhakar et al, 1993;Stahmann et al, 1994) and plants (Fischer and Bacher, 2006;Sandoval et al, 2008), not by animals. The autofluorescence property of riboflavin led to the assumption that riboflavin-producing bacterial colonies should also possess the property of autofluorescence.…”

Physiology, Biochemistry, and Applications of F420- and Fo-Dependent Redox Reactions

“…The deazaflavin and flavin biosynthetic pathways both proceed from the pyrimidine ribityldiaminouracil (5-amino-6-ribitylamino-2,4[1H,3H]-pyrimidinedione). In the flavin pathway, this substrate is condensed with 3,4-dihydroxy-2-butanone 4-phosphate to make a lumazine derivative (6,7-dimethyl-8-ribityllumazine) (69); two of these molecules subsequently condense to regenerate 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione with concomitant production of riboflavin (69). In the deazaflavin pathway, ribityldiaminouracil is instead condensed with the amino acid tyrosine (not 4-hydroxyphenylpyruvate as previously proposed [70]) leading to formation of F o (71).…”