Fig. 8
Carbon contribution of medium ingredients to riboflavin based on combined parallel 13C-labeled tracer studies using [13C2] glycine, [13C] formate, [13C5] glutamate, and [U13C] yeast extract. Riboflavin was synthesized by A. gossypii B2 grown on complex medium with rapeseed oil. Riboflavin was obtained at the end of the growth phase of riboflavin producing A. gossypii after 144 h. Data are derived from positional 13C enrichment obtained from 13C NMR measurements (Table 3), corrected for natural labeling and dilution effects through unlabeled pre-culture medium. Values denote carbon atoms and are normalized to 17 carbon atom influx into riboflavin. All values were multiplied by the number of carbon atoms of the reactants. Note that the model is simplified and cannot distinguish between carbon flux through e.g. gluconeogenesis or lower PP pathway as well as pyruvate dehydrogenase. Reaction between OAA/MAL and PEP/PYR pool is a lumped flux. Only reactions necessary for riboflavin biosynthesis were considered and all reactions represent net fluxes. Note that the conversion of citrate to isocitrate via aconitase most likely does not occur in the peroxisome [68]. 3PG, 3-phosphoplycerate; AcCoAP/M, peroxisomal/mitochondrial acetyl-CoA; AKG, α-ketoglutarate; ArP, 5-amino-6-ribitylamino-2,4(1H,3H)-pyrimidinedione; CH2-THF, 5,10-methylenetetrahydrofolate; CHO-THF, 10-formyltetrahydrofolate; FA, fatty acids (here: three C17.3 FA); FOR, formate; GAR, glycineamide ribonucleotide; GLU, glutamate; GLY, glycine; GLYINTR, intracellular glycine pool; GTP, guanosine triphosphate; PRA, 5-phosphoribosylamine; PYR, pyruvate; R5P, ribose 5-phosphate; Ru5P, ribulose 5-phosphate; RFV, riboflavin stored in the vacuole; SER, serine; THF, tetrahydrofolate; YE, yeast extract