FIG 2.

Redistribution of nitrogen from the three major nitrogen sources to proteinogenic amino acids during fermentation. Fermentations in which the total of arginine, glutamine, or ammonium was provided in ¹⁵N-labeled form were carried out, and the isotopic enrichment of each proteinogenic amino acid was measured. (A) Molar ratios of consumed to proteinogenic amino acids at different stages of fermentation. A value higher than 100% indicates that the amino acid is provided in the medium in excess of the requirements for protein synthesis. (B) Nitrogen amounts relating to the consumption of arginine, glutamine, ammonium, and other amino acids (gray). The bar on the left (T₀) shows the initial amounts of the three major nitrogen sources supplied in the medium. N_½, partial (one-half) nitrogen consumption; N_¾, partial (three-fourths) nitrogen consumption; N_T, complete nitrogen consumption; EF, end of fermentation. (C) Portion of nitrogen provided by arginine, glutamine, and ammonium recovered in proteinogenic amino acids (Ala, Gly, Val, Asp, Phe, Leu, Ile, Thr, Ser, Pro, Lys, His, Glu, and Arg). Nitrogen consumption (B) or incorporation (C) between the previous stage and the current stage is represented by dark colors, while the amount already consumed (B) or incorporated (C) at the previous stage is represented by light colors. (D) Contributions of nitrogen provided by consumed arginine, glutamine, and ammonium to the de novo synthesis of proteinogenic amino acids. The size of spheres is proportional to the isotopic enrichment of proteinogenic amino acids. The data were calculated using the averages of measured values from 2 or 8 independent biological experiments.