Peptides are biological molecules formed by the linkage of 2 to 50 amino acids. They perform a wide range of functions and are critically important in medicine, research, and industry. This guide provides a comprehensive overview of significant peptides, categorized by their primary biological system or function.
1. Endocrine Hormones & Regulators
These peptides circulate in the bloodstream to regulate complex physiological processes.
| Peptide Name | # of Amino Acids | Physiological/Clinical Significance |
|---|---|---|
| Insulin | 51 | Produced by pancreatic $\beta$-cells; lowers blood glucose levels. |
| Glucagon | 29 | Produced by pancreatic $\alpha$-cells; raises blood glucose levels. |
| Somatostatin | 14 | (Growth hormone-inhibiting hormone) Inhibits the release of GH, TSH, insulin, and glucagon. |
| Oxytocin | 9 | Hormone and neuropeptide; involved in childbirth, lactation, and social bonding. |
| Vasopressin (ADH) | 9 | (Antidiuretic Hormone) Regulates water reabsorption in the kidneys and blood pressure. |
| Calcitonin | 32 | Produced by the thyroid; lowers blood calcium levels. |
| Parathyroid Hormone (PTH) | 84 (Protein, but active fragment is 34) | Raises blood calcium levels (antagonist to Calcitonin). |
| Angiotensins | 7-10 | Angiotensin II is a potent vasoconstrictor that raises blood pressure. |
| Bradykinin | 9 | A potent vasodilator (lowers blood pressure) involved in inflammation. |
| Leptin | 167 (Protein, but often discussed with peptides) | Hormone of satiety; signals the brain to reduce appetite. |
| Ghrelin | 28 | The “hunger hormone”; stimulates appetite. |
| TRH | 3 | (Thyrotropin-releasing hormone) Stimulates release of TSH from the pituitary. |
| ACTH | 39 | (Adrenocorticotropic hormone) Stimulates the adrenal cortex to produce cortisol. |
2. Gastrointestinal (GI) Peptides
A specialized class of peptides that regulate all aspects of digestion and gut motility.
| Peptide Name | # of Amino Acids | Physiological/Clinical Significance |
|---|---|---|
| Gastrin | 17 (common) | Stimulates secretion of gastric acid (HCl) by the stomach. |
| Cholecystokinin (CCK) | 33 | Stimulates the pancreas to release digestive enzymes and the gallbladder to release bile. |
| Secretin | 27 | Stimulates the pancreas to release bicarbonate to neutralize stomach acid. |
| Motilin | 22 | Regulates migrating motor complex (MMC), controlling gut motility between meals. |
| Peptide YY (PYY) | 36 | Released from the small intestine after eating, it signals satiety to the brain. |
| GLP-1 | 30 or 31 | (Glucagon-like peptide-1) Enhances insulin secretion (incretin effect), a significant target for diabetes drugs. |
3. Neuropeptides
Peptides that function in the nervous system as neurotransmitters or neuromodulators.
| Peptide Name | # of Amino Acids | Physiological/Clinical Significance |
|---|---|---|
| Substance P | 11 | Key mediator of pain perception (nociception) and inflammation. |
| $\beta$-Endorphin | 31 | Endogenous opioid; powerful analgesic (pain reliever) and causes euphoria. |
| Enkephalins | 5 | (e.g., Leu- & Met-enkephalin) Endogenous opioids involved in pain regulation. |
| Neuropeptide Y (NPY) | 36 | One of the most potent appetite stimulants known; also involved in stress response. |
| Galanin | 29-30 | Involved in sleep, mood, appetite, and Alzheimer’s disease pathology. |
| CGRP | 37 | (Calcitonin gene-related peptide) Involved in vasodilation and migraine headaches. |
| Orexin (Hypocretin) | 33 & 28 | Critically involved in wakefulness and appetite. Lack of Orexin causes narcolepsy. |
4. Immune & Antimicrobial Peptides (AMPs)
Part of the innate immune system, these peptides provide a first line of defense against pathogens.
| Peptide Name | # of Amino Acids | Physiological/Clinical Significance |
|---|---|---|
| Defensins | 18-45 | (e.g., Human beta-defensin) Broad-spectrum antimicrobial activity (bacteria, fungi, viruses). |
| Cathelicidins (e.g., LL-37) | 37 | Antimicrobial and immune-modulating properties; involved in wound healing. |
| Gramicidin A | 15 | An antibiotic peptide (from Bacillus brevis) that forms ion channels in bacterial membranes. |
| Valinomycin | 12 (units) | An antibiotic (ionophore) that specifically transports potassium (K+) ions across membranes. |
| Polymyxin B | 10 | A “last-resort” antibiotic for multidrug-resistant Gram-negative bacteria; disrupts the outer membrane. |
5. Toxins & Venoms
Potent peptides, often used for defense or predation, that are invaluable in research.
| Peptide Name | # of Amino Acids | Physiological/Clinical Significance |
|---|---|---|
| $\alpha$-Amanitin | 8 | Deadly toxin from Amanita phalloides (death cap) mushroom; inhibits RNA polymerase II. |
| Microcystin | 7 (common) | Toxin from cyanobacteria (algal blooms); potent hepatotoxin (liver toxin). |
| Nodularin | 5 | Toxin from cyanobacteria, similar to Microcystin; liver toxin. |
| Melittin | 26 | Main component of bee venom; causes pain and inflammation by forming pores in cell membranes. |
| Conotoxins | 10-40 | A large family of toxins from cone snails; highly specific blockers of ion channels (used in research). |
| Chlorotoxin | 36 | From scorpion venom; blocks chloride channels and is studied for “painting” brain tumors. |
6. Cellular & Metabolic Peptides
Dipeptides and tripeptides with fundamental intracellular roles.
| Peptide Name | # of Amino Acids | Physiological/Clinical Significance |
|---|---|---|
| Glutathione (GSH) | 3 | The master antioxidant in all cells; protects against oxidative stress. |
| Creatine | 3 | (Not a peptide by bond, but functionally grouped) Stores high-energy phosphates in muscle. |
| Carnosine | 2 | A dipeptide in muscle and brain; acts as an antioxidant and pH buffer. |
7. Commercial & Synthetic Peptides
Peptides synthesized for specific commercial applications, from food to cosmetics.
| Peptide Name | # of Amino Acids | Physiological/Clinical Significance |
|---|---|---|
| Aspartame | 2 | Artificial sweetener (Aspartic acid + Phenylalanine). |
| Argireline | 6 | (Acetyl hexapeptide-3/8) A popular cosmetic peptide marketed as a topical alternative to Botox. |
| Copper Peptide (GHK-Cu) | 3 | Used in cosmetics for anti-aging and wound healing properties. |
| Semaglutide (Ozempic) | 31 | A synthetic analog of GLP-1, used to treat Type 2 diabetes and obesity. |
| Liraglutide (Victoza) | 31 | Another synthetic GLP-1 analog for diabetes and obesity treatment. |
Medically Reviewed by Zeinab Morshedi Yekta, M.D.
This article was medically reviewed for accuracy by Dr. Zeinab Morshedi Yekta. The content is based on scientific evidence and is intended to be educational. It does not replace professional medical advice.
Reference:
- Turito
- Walsh, G. (2014). Proteins: biochemistry and biotechnology. John Wiley & Sons.
- Lodish, H. F., Berk, A., Kaiser, C., Krieger, M., Bretscher, A., Ploegh, H. L., Martin, K. C., Yaffe, M. B., & Amon, A. (2021). Molecular cell biology (Ninth edition, loose-leaf student edition.). Macmillan Learning.
- Whitford, D. (2013). Proteins: structure and function. John Wiley & Sons.
- Petersen, M. C., & Shulman, G. I. (2018). Mechanisms of insulin action and insulin resistance. Physiological reviews.
- Boldyrev, A. A., Aldini, G., & Derave, W. (2013). Physiology and pathophysiology of carnosine. Physiological reviews.
-
Kim, S., Chen, J., Cheng, T., Gindulyte, A., He, J., He, S., Li, Q., Shoemaker, B. A., Thiessen, P. A., Yu, B., & Bolton, E. E. (2023). PubChem 2023 update. Nucleic Acids Research, 51(D1), D1373–D1380. https://doi.org/10.1093/nar/gkac956
- UniProt: the Universal Protein Knowledgebase. Nucleic Acids Research, 51(D1), D523–D531. https://doi.org/10.1093/nar/gkac1052
