Advance in Riboflavin Biosynthesis: Fermentation Techniques, Enzymatic Pathways, Utilisation and Industrial Applications

Two molecules of ribulose 5-phosphate and one molecule of GTP are needed as substrates for the production of one riboflavin molecule. GTP's imidazole ring is hydrolytically opened to produce a 4,5-diaminopyrimidine, which is then followed by deamination, side chain reduction, and dephosphorylation to produce 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione. 6,7-dimethyl-8-ribityllumazine is produced by condensing 5-amino-6-ribitylamino2,4(1H,3H)-pyrimidinedione with 3,4-dihydroxy-2-butanone 4-phosphate, which is derived from ribulose 5-phosphate. Riboflavin and 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione are produced upon dismutation of the lumazine derivative and are then recycled throughout the biosynthetic process. Many studies have been conducted on the structure of the biosynthetic enzyme 6,7-dimethyl-8-ribityllumazine synthase. Under the direction of the inducible Pxyl promoter in B. subtilis PY, overexpression of glucose-6-phosphate dehydrogenase (G6PDH) altered carbon flow in Bacillus subtilis through the pentose phosphate (PP) pathway. The yield of riboflavin and the availability of ribulose-5-phosphate (Ru5P) will change if the carbon input into the PP pathway is altered. The specific growth rate remained constant, but the glucose consumption rate significantly increased as a result of overexpres¬sion of G6PDH. A 25%±2 increase in riboflavin synthesis was achieved. Lower acid production (acetate andpyruvate) and higher acetoin formation were noted in comparison to by-product formation in flask culture. The results of metabolic studies and carbon flux redistribution showed that overexpression of G6PDH increases the fluxes in the PP pathway.