Peptide Classification System
By Length
| Classification | Residue Count | Examples | MW Range (Da) |
|---|---|---|---|
| Dipeptide | 2 | Carnosine, Anserine | 200–300 |
| Tripeptide | 3 | Glutathione, thyrotropin-releasing hormone | 300–500 |
| Tetrapeptide | 4 | Angiotensin II (fragment), kyotorphin | 400–600 |
| Pentapeptide | 5 | Enkephalins, tuftsin | 500–700 |
| Hexapeptide | 6 | ACE inhibitors (fragment) | 600–800 |
| Heptapeptide | 7 | Substance P (fragment) | 700–900 |
| Octapeptide | 8 | Vasopressin, oxytocin (cyclic) | 800–1100 |
| Nonapeptide | 9 | Oxytocin, vasopressin | 1000–1200 |
By Function
Neuropeptides
Signaling molecules in the nervous system. Include endorphins, enkephalins, substance P, and neuropeptide Y.
Hormonal Peptides
Regulate physiological processes. Include insulin, glucagon, oxytocin, and growth hormone-releasing hormone.
Antimicrobial Peptides
Innate immune defense. Include defensins, cathelicidins, and magainins.
Antioxidant Peptides
Protect against oxidative stress. Include glutathione, carnosine, and erogothioneine.