Studies on the biosynthesis of riboflavin. Nitrogen metabolism and flavinogenesis in Eremothecium ashbyii

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Abstract
Eremothecium ashbyii grown on a basal glucose-salts-vitamins medium supplemented with 0.24% (w/v) peptone is fully grown after 5 days but continues to produce riboflavin up to 7-8 days. Maximal concentration of riboflavin is obtained over the range of 0.16-0.40% (w/v) peptone. Using the basal medium supplements with 0.005% (w/v) peptone N, addition of L-threonine, L-serine or L-tyrosine specifically stimulated riboflavin synthesis; L-tyrosine was the least effective. D-Threonine was inactive. L-Glutamate, L-aspartate and L-asparagine stimulated both growth and flavinogenesis, while L-cysteine inhibited both. Other amino acids tested were without obvious effect on riboflavin synthesis, but some inhibited growth slightly. Under the same conditions the purines xanthine and adenine, and adenosine, stimulated flavinogenesis while most pyrimi-dines and their derivatives were without effect, although alloxan inhibited both growth and riboflavin synthesis. At very high concentrations, uracil inhibited riboflavin synthesis, although it did not inhibit the adenine-stimulated production of riboflavin. Neither 5:6-dimethylbenziminazole nor l:2-dimethyl-4-amino-5 (D - 1[image] - ribitylamino) benzene stimulated riboflavin production under the same conditions. Of the other N-containing compounds tested, urea in low concentrations occasionally stimulated and (NH4)2SO4 was without effect. D-Glucosamine was a powerful inhibitor of both growth and riboflavin. The effects of the stimulatory amino acids are not cumulative, while those of a purine and an amino acid are. The significance of these results in relation to the problem of the biosynthesis of riboflavin is discussed.