Figure 10.

Ultrafast COSY spectrum of a biomass hydrolysate from E. coli cells grown on a 1:1 [U-¹³C]-glucose:glucose mixture (12 g/L). The sample contains mainly amino acids released from the hydrolysis of cellular proteins. The spectrum was recorded in 20 s (4 scans) on a 500 MHz spectrometer equipped with a cryoprobe. Cross-peaks are annotated according to the corresponding carbon in the amino acids, using the international one-letter code for amino-acids and using standard letters for the position of the protonated carbon in the molecular backbone, i.e., A, B, G, D, and E for α, β, γ, δ, and ε, respectively. Site-specific ¹³C isotopic enrichments are measured by extracting columns from the 2D spectrum and by integrating the satellites of the resulting site-specific patterns.