Fig. 1.

Estimation of glucose and protein costs of synthesizing amino acids. (A) The modeling framework to estimate substrate and protein costs of synthesizing a metabolite of interest. By directing the flux from the substrate to the metabolite—for example, maximizing the metabolite synthesis rate (v_met) while fixing the substrate uptake rate (v_sub)—all the involved reactions and their rates (v_i) can be obtained. In addition, the total protein mass (v_pm) that supports the flux distribution can be obtained, which is the sum of the products of rates (v_i) and protein costs (pc_i) of individual reactions. (B) The comparison between estimated glucose costs and previously reported energy costs of synthesizing amino acids (12). (C) The comparison between estimated glucose and protein costs of synthesizing amino acids. Amino acids are shown by one-letter abbreviations. Energy cost: high-energy phosphate bond consumed per amino acid synthesized. Glucose cost: glucose consumed per amino acid synthesized. Protein cost: protein mass (gram protein per gram cell dry weight) required per amino acid biosynthetic flux.