Table 1.
Distribution of unique tryptic peptides and tryptic peptides containing the N-X-T/S motif over subcellular classes of proteins in the human protein (IPI) database
| Tryptic peptidesa | Peptides containing N-X-T/S | |||
| Number of peptidesa | Number of proteins | Number of peptidesa | Number of proteins | |
| Intracellular | 510,685(68.2%b) | 26,721(66.6%c) | 32,770(4.4%b) | 17,475(43.6%c) |
| Secreted | 80,069(10.7%) | 3,772(9.4%) | 7,195(1.0%b) | 2,772(6.9%c) |
| Transmembrane | 114,282(15.3%) | 6,375(15.9%) | 10,359(1.4%) | 4,645(11.6%) |
| Cell surface | 70,126(9.4%) | 3,242(8.1%) | 5,138(0.7%) | 2,166(5.4%) |
| All extracellular | 264,477(35.5%) | 13,389(33.4%) | 22,692(3.0%) | 9,583(23.9%) |
| Total protein | 749,163(100%) | 40,110(100%) | 52,442(7.0%) | 27,058(67.5%) |
The human International Protein Index (IPI) database (version 2.28) contains a total of 40,110 protein entries. aTryptic peptides are defined as peptide sequences that end with Arg or Lys, are not followed by proline, and fall within the mass range from 500 to 5000 Da. bThe percentage represents the fraction of total tryptic peptides from the human database (749,163). cThe percentage represents the fraction of total proteins from the human database (40,110).