Fig. 2

Accuracy and precision of ¹³C atom% quantification by Sipros 4 on the PSM level for standard E. coli samples. The atom% estimates for all PSMs identified by Sipros 4 in each E. coli proteome are shown in its corresponding histogram with 1-atom% bin width. The medians of the atom% histograms are exactly aligned to their expected atom% values marked by the red vertical line, which indicates accurate ¹³C atom% quantification by Sipros 4 across the full range of ¹³C enrichment levels. The dispersion of the atom% histograms measures the precision of ¹³C atom% quantification, which decreases gradually from the unlabeled sample to the 50% ¹³C-labeled sample and then increases in the 99% ¹³C-labeled sample. The size of atom% histograms reflects the number of identified PSMs, which ranges from 26,583 PSMs in the 99% ¹³C-labeled sample to 64,113 PSMs in the unlabeled sample