Fig. 3

Incorporation of CO₂ into cellular proteins. The intermediates of the TCA cycle, oxaloacetate and α-ketoglutarate, are metabolized to produce various amino acids, which are subsequently incorporated into cellular proteins. Isotopic labeling experiments using ¹³CO₂ demonstrate the preferential synthesis of proteinogenic amino acids in transgenic E. coli K12. Data are presented as means ± standard deviation, with n = 3 independent biological samples. A two-tailed t-test was used for statistical analysis, **** indicates p < 0.005 (highly statistically significantly difference); *** indicates p < 0.01; ** indicates p < 0.05 (statistically significantly difference); * indicates p < 0.1 (borderline statistically significantly difference). Strains were supplemented with 10% ¹³CO₂ and 90% H₂, with 10% of ¹³CO₂ replenished every 12 h during the 48 h incubation. Isotopic enrichments derived from ¹³CO₂ are detected in the M + 1 specie of various amino acids. The labeled ¹³CO₂ are marked in red asterisk * marks. Hetero-expressed enzymes KOR and ACL are indicated in purple and yellow, respectively