The immediate nucleotide precursor, guanosine triphosphate, in the riboflavin biosynthetic pathway.

Biosynthesis of Riboflavin, Folic Acid, Thiamine, and Pantothenic Acid

“…However, recent evidence has clearly shown that this group is derived from the ribose moiety of GTP. This has been established by studies on the incorporation of I4C-labeled species of guanosine into riboflavin in S. typhimurium (9, P. guillieimondii (13,14) E. ashbyii (7,15), and B. subtilis (8) and decisively confirmed with the discoveries of enzymes from various sources that catalyze the reduction of the nucleotidyl ribose group (13,16,17). The earlier contention that ribitol and ribose are preferentially incorporated into the ribityl group of riboflavin (1 [8][9][10][11][12][13][14][15][16][17][18][19][20] was based on studies with whole cells under conditions in which the effects of pool sizes were hard to interpret and thus the conclusions were suspect.…”

“…This not only established that guanosine or a guanine nucleotide is the precursor, but it also indicated that the ribose portion of such a compound is retained and converted metabolically to the ribityl group of riboflavin. Supporting evidence was supplied by Mitsuda and coworkers (6,7), who concluded that GTP is the precursor through their analyses of the nucleoside and nucleotide pools of Eromothecium ashbyii under various conditions of flavinogenesis, and by Bresler et al (8), who presented evidence for a role for a guanosine compound as the precursor in Bacillus subtilis. The *Earlier reviews on the biosynthesis of the water-soluble vitamins have appeared (la, lb).…”

Formation of 4-ribitylamino-5-amino-2,6-dihydroxypyrimidine in an adenine-riboflavin doubleless mutant of Bacillus subtilis.

“…The authors showed with a high flavinogenic mold, Eremothecium ashbyii, that xanthine is a most efficient precursor of purines (1)(2)(3) and guanosine triphos phate is a most direct precursor of purines, nucleosides, and nucleotides in the riboflavin biosynthetic pathway (4,5). The nucleotide, after rupture of the imida zole ring at C(8) (6), appears to be converted to 6,7-dimethyl-8-ribityllumazine which was proved to be the immediate intermediate to riboflavin (7,8).…”