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.
Melittin has two distinct halves: residues 1–18 are largely hydrophobic, while the C-terminal KRKRQQ tail is strongly cationic. The charged tail binds the negatively charged membrane surface and the hydrophobic stretch inserts into the bilayer, which is how melittin disrupts cell membranes. A window of 9 is the size Kyte and Doolittle recommended for mapping hydrophobic and hydrophilic regions; transmembrane prediction uses a window of 19. This plot is the unmodified output of the tool below.
Run your own sequence →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. Calculated for the linear peptide with free termini; the companion guide shows how to correct for disulfides, amidation and other modifications.
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 food. Some form during processing or fermentation, others are released when digestive enzymes break down food proteins. Food chemists study them for what they contribute to flavour, texture and the chemistry of digestion.
Casein releases many short peptides during digestion and fermentation. Proline-rich tripeptides such as Ile-Pro-Pro and Val-Pro-Pro resist further digestion and inhibit angiotensin-converting enzyme in vitro.
Fermentation is a powerful peptide generator. Aged cheeses accumulate small peptides that shape their savoury and bitter taste; soy sauce and miso owe much of their umami to free amino acids and short peptides.
Collagen's triple helix is built from Gly-X-Y repeats, where Y is often hydroxyproline. Digested gelatin releases Pro-Hyp and Hyp-Gly, dipeptides that resist further breakdown.
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.
Long-form guides to what the calculators compute, the chemistry and biology behind them, and how peptides are made, analysed and handled. Every worked example can be reproduced with the tools above.
How peptide mass is built from residue masses, and how disulfides, amides and counterions change it.
Read →Henderson–Hasselbalch step by step, why calculators disagree, and pI in the lab.
Read →Window size, the transmembrane threshold, GRAVY, and where hydropathy plots mislead.
Read →Two chains, three disulfides: discovery, biosynthesis from proinsulin, hexamers, and engineered analogues.
Read →Enkephalins, endorphins and dynorphins: the YGGF motif, three precursors, and what endorphins are not.
Read →The dipeptide sweetener: why the methyl ester matters, how it degrades, and peptides in taste.
Read →Charge, amphipathicity and the helical wheel, how AMPs kill bacteria, selectivity and resistance.
Read →A lantibiotic food preservative: thioether rings, lipid II binding, and why calculators cannot handle it.
Read →ESI and MALDI, tandem MS, and how to read b and y fragment ions, with a worked example.
Read →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 cone snail Conus geographus releases a fast-acting insulin into the water around a school of fish, which become sluggish and easy to engulf. Its insulin lacks the regions that let ours pack into slow-dissolving hexamers. More on cone snails →