Histogram showing the number of proteins identified versus the number of validated, non-redundant peptides found for each protein, across all experiments. The number of validated, non-redundant peptides used to identify each protein was calculated and the proteins with identical numbers of peptides were plotted in the same group, indicated on the X-axis. For example, there are a total of 70 proteins that were identified with a single peptide. The inset depicts in detail the number of proteins that were identified with 1–20 peptides. Proteins identified with more than 20 peptides were categorized into groups as indicated.