Calculate molecular weight, isoelectric point and hydrophobicity for any amino acid sequence. Search a database of 89+ characterised peptides. Read reference material on the peptides in your body, your food, and the natural world.
Six tools that run entirely in your browser — no registration, no sequence upload to a server. Paste a one-letter or three-letter sequence and get numbers back immediately. Built for students, lab work, and anyone who needs a quick calculation without opening a full bioinformatics suite.
Monoisotopic and average MW, empirical formula, and net charge at pH 7.4. Handles the 20 standard amino acids plus common modifications such as C-terminal amidation and N-terminal acetylation.
Open calculator →The pH at which a peptide carries zero net charge, from side-chain pKa values for the ionisable residues plus the free termini. Useful for planning ion-exchange purification or predicting solubility minima.
Open calculator →Kyte-Doolittle hydropathy profile with an adjustable sliding window, so you can locate membrane-spanning stretches and exposed hydrophilic loops. Defaults to a 9-residue window.
Open tool →More than 89 characterised peptides with sequence, length, molecular weight, biological source and functional class. Filter by any field, or sort by mass to find candidates in a given range.
Browse database →All 20 proteinogenic amino acids in one table: codes, residue mass, side-chain pKa where applicable, Kyte-Doolittle index, polarity class, and structural notes.
Open reference →Converts between one-letter and three-letter notation in both directions, tolerating hyphens, spaces and line breaks. Handy when moving sequences between papers, catalogues and analysis software.
Open converter →A peptide is a chain of amino acids joined by amide (peptide) bonds — the same building blocks and the same linkage that make up proteins. The distinction is one of size and convention rather than chemistry: chains up to roughly 50 residues are usually called peptides, longer ones proteins. The boundary is soft. Insulin, at 51 residues across two chains, is described as a peptide hormone in most of the literature.
Despite their small size, peptides cover an extraordinary functional range. They act as hormones, antibiotics, neurotransmitters, immune signals and toxins. Many are not simple linear chains: they can be cyclic, contain disulfide bridges, carry non-standard residues, or be linked through side chains rather than the α-amino group. Your body produces thousands of distinct peptides, coordinating processes from digestion to immunity.
Known as the "love hormone," oxytocin is a nonapeptide produced in the hypothalamus. It plays a central role in social bonding, trust, and childbirth — and is one of the most studied peptides in neuroscience.
The human genome encodes thousands of bioactive peptides that carry out indispensable roles — from regulating blood glucose after a meal to transmitting pain signals in milliseconds. Six of the major functional classes are outlined below.
The body's chemical messengers. Insulin (51 AA, from pancreatic β-cells) regulates blood glucose after meals; glucagon (29 AA) raises it when levels drop. Oxytocin (9 AA) triggers uterine contractions and milk ejection, and plays a key role in social bonding. These hormones act at nanomolar concentrations.
Peptides that transmit or modulate signals in the nervous system. β-Endorphin (31 AA), released during intense exercise, binds opioid receptors and produces natural pain relief. Enkephalins (5 AA: Met-YGGFM and Leu-YGGFL) are the brain's endogenous analgesics. Substance P (11 AA) amplifies pain signals.
The innate immune system's first line of defense. Human β-defensins (18–45 AA) punch holes in bacterial membranes. Cathelicidin LL-37 (37 AA) is active against bacteria, fungi, and enveloped viruses. Over 3,000 natural antimicrobial peptides have been catalogued — a major focus in antibiotic resistance research.
Peptides that orchestrate digestion. Cholecystokinin (CCK, 33 AA) triggers gallbladder contraction and pancreatic enzyme release. Secretin (27 AA) prompts bicarbonate release to neutralise stomach acid. Ghrelin (28 AA), produced in the stomach, is the primary hunger signal before meals.
Atrial natriuretic peptide (ANP, 28 AA) lowers blood pressure by promoting sodium excretion by the kidneys. Bradykinin (9 AA) dilates blood vessels. Angiotensin II (8 AA) is a potent vasoconstrictor; drugs that block its formation (ACE inhibitors) are among the most widely prescribed medicines worldwide.
Thymosin α1 (28 AA), secreted by the thymus, promotes T-cell maturation and has been used clinically to boost immune responses. Thymulin (9 AA) is essential for T-cell development. Tuftsin (4 AA: Thr-Lys-Pro-Arg), cleaved from immunoglobulin G, stimulates macrophage phagocytic activity.
Many of the peptides you encounter aren't made by your body — they're in your diet. Some form during food processing or fermentation, others are released when digestive enzymes break down food proteins.
Casein (~80% of milk protein) releases bioactive peptides during digestion. β-Casomorphins (7 AA) bind opioid receptors in the gut. Lactotripeptides IPP (Ile-Pro-Pro) and VPP (Val-Pro-Pro), concentrated in fermented dairy, are well-characterised ACE inhibitors studied in clinical trials as natural antihypertensives.
Fermentation is a powerful peptide generator. Aged cheeses accumulate ACE-inhibitory peptides over months. Japanese natto contains nattokinase (a fibrin-cleaving enzyme) plus antioxidant peptides from soy proteins. Soy sauce and miso, produced by Aspergillus fermentation, are rich in short peptides and glutathione precursors.
Collagen's triple helix is built from Gly-X-Y repeats, where X is often proline and Y is hydroxyproline (Hyp). Digestive enzymes release characteristic peptides — especially Pro-Hyp and Hyp-Gly — from collagen-rich foods. Stable-isotope labelling studies show these peptides are absorbed intact and appear in blood within 1–2 hours.
In normal digestion, gluten proteins are fully broken down. In celiac disease, a single gliadin fragment — the 33-mer (33 AA) — resists all human digestive enzymes and triggers an immune cascade in the small intestine; it is considered the primary immunogenic driver of the disease. Wheat exorphins, opioid-like peptides from gluten digests, have also been characterised biochemically.
From scorpion venom to the cocoa in your chocolate — peptides shape the natural world in remarkable ways. Four longer reference sections cover the ground in detail.
Venoms, silk, frog secretions — how the animal kingdom uses peptides as weapons and signals.
Explore →From Fischer's 1901 synthesis to Nobel Prizes, blockbuster drugs, and modern solid-phase synthesis.
Read →The most toxic, most expensive, longest, fastest-acting — the extremes of the peptide world.
See records →Clear definitions of 100+ peptide science terms, explained without excessive jargon.
Browse glossary →Fermentation and roasting of cacao beans break storage proteins into short peptides. These fragments are precursors of chocolate flavour and have been studied for antioxidant activity.
Spider dragline silk is made of spidroin proteins — long polypeptide chains with repeating glycine and alanine motifs. The alanine blocks form crystalline β-sheets that give silk its tensile strength.
The molecule associated with bonding and trust is a nonapeptide — nine amino acids, closed into a ring by a disulfide bridge between residues 1 and 6, with a three-residue tail.
The gut and brain communicate through peptide hormones. Ghrelin rises before meals and signals hunger; GLP-1, released after eating, signals satiety — the same receptor targeted by a well-known class of modern drugs.