Fig. 6

Experimental ¹³C enrichment of riboflavin produced on [¹³C₅] glutamate (a) and fully ¹³C-labeled yeast extract (b) measured via ¹³C NMR. The initial naturally labeled medium was replaced by medium containing ¹³C-labeled yeast extract via centrifugation after 32 h of cultivation. The fully ¹³C-labeled glutamate replaced the naturally labeled glutamate in the medium at the beginning of a parallel experiment with otherwise naturally labeled medium compounds. The circles of the riboflavin molecules depict carbon atoms. Colored circles denote the part of the riboflavin molecule under investigation. The colors purple and light blue in the bar charts represent the percentage originating from the respective ¹³C-labeled precursor, while the grey bars indicate origin from a different medium ingredient. Data denote values from three independent experiments with a mean standard deviation of 5%