Peptides
| Definition | Short chains of amino acids |
|---|---|
| Size Range | 2-50 amino acids |
| Bond Type | Peptide bonds |
| Related To | Proteins, amino acids |
| Examples | Insulin, oxytocin, endorphins |
Peptides are short chains of amino acids linked by peptide bonds. They are distinguished from proteins primarily by their shorter length, typically containing between 2 and 50 amino acids. Peptides play crucial roles in biological processes, acting as hormones, neurotransmitters, growth factors, and signaling molecules throughout the body.
Structure and Formation
The Peptide Bond
Peptides are formed when the carboxyl group (-COOH) of one amino acid reacts with the amino group (-NH2) of another, releasing a water molecule (condensation reaction). The resulting covalent bond is called a peptide bond.
Classification by Size
| Type | Amino Acids | Examples |
|---|---|---|
| Dipeptide | 2 | Carnosine, anserine |
| Tripeptide | 3 | Glutathione, TRH |
| Oligopeptide | 2-20 | Oxytocin (9), vasopressin (9) |
| Polypeptide | 20-50 | Insulin chains, ACTH |
| Protein | >50 | Hemoglobin, enzymes |
Types of Peptides
Endogenous Peptides
Naturally produced peptides in the human body include:
Hormonal Peptides
- Insulin: Regulates blood glucose (51 amino acids)
- Glucagon: Raises blood glucose (29 amino acids)
- Growth Hormone Releasing Hormone (GHRH): Stimulates GH release
- Oxytocin: Social bonding, uterine contractions (9 amino acids)
- Vasopressin (ADH): Water balance regulation (9 amino acids)
Neuropeptides
- Endorphins: Natural pain relief, reward
- Enkephalins: Pain modulation
- Substance P: Pain transmission
- Neuropeptide Y: Appetite regulation
Antimicrobial Peptides
- Defensins: Innate immune defense
- Cathelicidins: Broad-spectrum antimicrobials
Synthetic Peptides
Peptides created for research and therapeutic purposes:
- BPC-157 – Research peptide for tissue healing
- TB-500 – Synthetic thymosin beta-4
- Semaglutide – Modified GLP-1 for diabetes/weight
- Ipamorelin – Growth hormone secretagogue
Biological Functions
Cell Signaling
Peptides serve as critical messengers in cellular communication:
- Bind to specific receptors on cell surfaces
- Trigger intracellular signaling cascades
- Regulate gene expression
- Coordinate tissue responses
Hormonal Regulation
Many hormones are peptides that regulate:
- Metabolism and energy balance
- Growth and development
- Reproduction
- Stress responses
- Water and electrolyte balance
Immune Function
Peptides play essential roles in immunity:
- Direct antimicrobial activity
- Immune cell communication (cytokines)
- Inflammation regulation
- Wound healing coordination
Research Applications
Research Peptide Categories
Growth Hormone Peptides
Compounds that stimulate growth hormone release:
- GHRH analogs (Sermorelin, CJC-1295, Tesamorelin)
- GHRPs (GHRP-2, GHRP-6, Hexarelin)
- Ipamorelin
Healing and Recovery Peptides
Metabolic Peptides
- GLP-1 agonists (Semaglutide, Tirzepatide)
- Melanotan peptides
Peptide Synthesis
Solid-Phase Peptide Synthesis (SPPS)
The most common method for peptide production, developed by Bruce Merrifield (Nobel Prize, 1984):
- Anchor first amino acid to solid resin
- Sequentially add protected amino acids
- Remove protecting groups after each addition
- Cleave completed peptide from resin
- Purify using HPLC
Recombinant Production
Larger peptides and proteins are often produced using:
- Bacterial expression (E. coli)
- Yeast expression systems
- Mammalian cell culture
Peptide Therapeutics
Peptides offer advantages as therapeutic agents:
Advantages
- High specificity and potency
- Lower toxicity than small molecules
- Predictable metabolism
- Fewer drug-drug interactions
Challenges
- Poor oral bioavailability
- Short half-life (enzymatic degradation)
- Manufacturing complexity
- Storage requirements (often refrigeration)
FDA-Approved Peptide Drugs
| Drug | Type | Indication |
|---|---|---|
| Insulin | Hormone | Diabetes |
| Semaglutide | GLP-1 agonist | Diabetes, obesity |
| Tesamorelin | GHRH analog | HIV lipodystrophy |
| Octreotide | Somatostatin analog | Acromegaly, carcinoid |
| Leuprolide | GnRH analog | Prostate cancer, endometriosis |
Handling and Storage
Peptides require careful handling:
- Lyophilized (powder): Store at -20°C or colder, stable for years
- Reconstituted: Refrigerate (2-8°C), use within weeks
- Avoid: Repeated freeze-thaw cycles, heat, direct sunlight
- Reconstitution: Use bacteriostatic water for multi-dose vials
Related Topics
- Amino Acids – Building blocks of peptides
- Proteins – Larger polypeptide chains
- Growth Hormone Peptides – GH secretagogues
- Peptide Bonds – Chemical structure
References
- Nelson DL, Cox MM. "Lehninger Principles of Biochemistry." 8th ed. W.H. Freeman; 2021.
- Fosgerau K, Hoffmann T. "Peptide therapeutics: current status and future directions." Drug Discov Today. 2015.
- Lau JL, Dunn MK. "Therapeutic peptides: Historical perspectives, current development trends, and future directions." Bioorg Med Chem. 2018.