Melittin

A 26-residue amide from honeybee venom: a largely hydrophobic N-terminal region and a strongly basic C-terminus. A common test peptide in mass spectrometry and membrane studies. Every value on this page is calculated from the structure shown, by the method and constants in the sources below; measured values for a particular lot are on its certificate of analysis.

Structure

Three-letter code: H-Gly-Ile-Gly-Ala-Val-Leu-Lys-Val-Leu-Thr-Thr-Gly-Leu-Pro-Ala-Leu-Ile-Ser-Trp-Ile-Lys-Arg-Lys-Arg-Gln-Gln-NH2

One-letter code: GIGAVLKVLT TGLPALISWI KRKRQQ

• 26 residues
• N-terminus: free amine
• C-terminus: amide

Calculated properties

Calculated from the structure

Property	Value
Molecular formula	C131H229N39O31
CAS Registry Number	20449-79-0
Average molecular weight	2,846.52 g/mol
Monoisotopic mass	2,844.7542 Da
Net charge at pH 7	6.0
Isoelectric point	No acidic groups: the peptide carries a positive charge at every pH, so it has no isoelectric point.
Molar absorption coefficient, 280 nm	5,500 M−1 cm−1
Hydropathy (GRAVY)	0.27

Net charge across the pH range

pH 2	pH 4	pH 6	pH 7	pH 8	pH 10	pH 12
6.0	6.0	6.0	6.0	5.8	4.6	1.7

Composition: Leu 4, Gly 3, Ile 3, Lys 3, Ala 2, Arg 2, Gln 2, Thr 2, Val 2, Pro 1, Ser 1, Trp 1.

Expected mass spectrometry ions

The protonated ions expected in positive-mode electrospray, from the monoisotopic mass, and the common sodium and potassium adducts. MALDI spectra show mainly [M+H]⁺.

Expected ions (monoisotopic)

Ion	m/z
[M+H]+	2,845.7614
[M+2H]2+	1,423.3844
[M+3H]3+	949.2587
[M+4H]4+	712.1958
[M+5H]5+	569.9581
[M+Na]+	2,867.7434
[M+K]+	2,883.7173

Isotope pattern

Natural carbon-13, nitrogen-15, oxygen-18, sulfur-34 and deuterium spread each ion over a cluster of peaks about 1 Da apart (1/z on the m/z scale). For a molecule this size the monoisotopic peak is not the tallest: the most abundant is M+1. A spectrum read at its tallest peak, or a deconvoluted mass from it, sits about 1.00 Da above the monoisotopic mass.

Isotope peaks (relative abundance, most abundant = 100)

Peak	Abundance	Neutral mass	[M+H]+	[M+2H]2+	[M+3H]3+	[M+4H]4+	[M+5H]5+
M (monoisotopic)	62.6	2,844.7542	2,845.7614	1,423.3844	949.2587	712.1958	569.9581
M+1	100.0	2,845.7570	2,846.7643	1,423.8858	949.5929	712.4465	570.1587
M+2	83.4	2,846.7598	2,847.7671	1,424.3872	949.9272	712.6972	570.3592
M+3	48.1	2,847.7625	2,848.7698	1,424.8885	950.2614	712.9479	570.5598
M+4	21.5	2,848.7652	2,849.7725	1,425.3899	950.5957	713.1986	570.7603
M+5	8.0	2,849.7678	2,850.7751	1,425.8912	950.9299	713.4492	570.9608
M+6	2.5	2,850.7704	2,851.7777	1,426.3925	951.2641	713.6999	571.1614
M+7	0.7	2,851.7730	2,852.7803	1,426.8938	951.5983	713.9505	571.3619

Fragment ions (MS/MS)

Collision-induced fragmentation breaks peptide bonds along the backbone. Fragments that keep the N-terminus are b ions; those that keep the C-terminus are y ions. Reading the ladder confirms the sequence residue by residue. Singly charged monoisotopic values, with doubly charged values beside them. The b ion containing every residue is rarely seen and the y ion containing every residue is the precursor itself, so neither is listed.

b and y ions

b#	b+	b2+	Residue	y+	y2+	y#
1	58.0287	29.5180	Gly	—	—	26
2	171.1128	86.0600	Ile	2,788.7400	1,394.8736	25
3	228.1343	114.5708	Gly	2,675.6559	1,338.3316	24
4	299.1714	150.0893	Ala	2,618.6345	1,309.8209	23
5	398.2398	199.6235	Val	2,547.5973	1,274.3023	22
6	511.3239	256.1656	Leu	2,448.5289	1,224.7681	21
7	639.4188	320.2130	Lys	2,335.4449	1,168.2261	20
8	738.4872	369.7473	Val	2,207.3499	1,104.1786	19
9	851.5713	426.2893	Leu	2,108.2815	1,054.6444	18
10	952.6190	476.8131	Thr	1,995.1974	998.1024	17
11	1,053.6667	527.3370	Thr	1,894.1497	947.5785	16
12	1,110.6881	555.8477	Gly	1,793.1021	897.0547	15
13	1,223.7722	612.3897	Leu	1,736.0806	868.5439	14
14	1,320.8249	660.9161	Pro	1,622.9965	812.0019	13
15	1,391.8621	696.4347	Ala	1,525.9438	763.4755	12
16	1,504.9461	752.9767	Leu	1,454.9067	727.9570	11
17	1,618.0302	809.5187	Ile	1,341.8226	671.4149	10
18	1,705.0622	853.0347	Ser	1,228.7385	614.8729	9
19	1,891.1415	946.0744	Trp	1,141.7065	571.3569	8
20	2,004.2256	1,002.6164	Ile	955.6272	478.3172	7
21	2,132.3206	1,066.6639	Lys	842.5431	421.7752	6
22	2,288.4217	1,144.7145	Arg	714.4482	357.7277	5
23	2,416.5166	1,208.7620	Lys	558.3471	279.6772	4
24	2,572.6177	1,286.8125	Arg	430.2521	215.6297	3
25	2,700.6763	1,350.8418	Gln	274.1510	137.5791	2
26	—	—	Gln	146.0924	73.5498	1

Immonium ions (low-mass markers of the residues present): Gly 30.0338, Ala 44.0495, Ser 60.0444, Pro 70.0651, Val 72.0808, Thr 74.0600, Ile 86.0964, Leu 86.0964, Gln 101.0709, Lys 101.1073, Arg 129.1135, Trp 159.0917.

What to watch for analytically

Variants this sequence can give, from its chemistry. They are what an HPLC or mass spectrometry result for this peptide is read against; none is a statement about a particular lot. Where synthesis variants come from is explained in How synthetic peptides are made.

Sequence-specific variants

Variant	Mass change	Why
Tryptophan oxidation	+15.995 or +31.990 Da	Tryptophan at position 19 can oxidize, particularly on exposure to light and air.
Glutamine deamidation	+0.984 Da	Glutamine at positions 25 and 26 can also deamidate, much more slowly than asparagine.
C-terminal amide	free-acid variant +0.984 Da	The C-terminus is an amide. The corresponding free acid, from synthesis or hydrolysis, differs by +0.984 Da, close to the isotope spacing, so it needs a resolved spectrum to tell apart.
Synthesis-related variants	e.g. +252.082 Da (Pbf), minus a residue (deletion)	As for any synthetic peptide, deletion sequences and incompletely deprotected forms can occur; on arginine, a residual Pbf protecting group adds 252.082 Da.

Sources & Further Reading

1. Prohaska T, Irrgeher J, Benefield J, Böhlke JK, Chesson LA, Coplen TB, et al. Standard atomic weights of the elements 2021 (IUPAC Technical Report). Pure and Applied Chemistry 2022;94(5):573–600. doi:10.1515/pac-2019-0603
2. Wang M, Huang WJ, Kondev FG, Audi G, Naimi S. The AME 2020 atomic mass evaluation (II). Tables, graphs and references. Chinese Physics C 2021;45(3):030003. doi:10.1088/1674-1137/abddaf
3. Rice P, Longden I, Bleasby A. EMBOSS: the European Molecular Biology Open Software Suite. Trends in Genetics 2000;16(6):276–277. doi:10.1016/S0168-9525(00)02024-2
4. Pace CN, Vajdos F, Fee L, Grimsley G, Gray T. How to measure and predict the molar absorption coefficient of a protein. Protein Science 1995;4(11):2411–2423. doi:10.1002/pro.5560041120
5. Kyte J, Doolittle RF. A simple method for displaying the hydropathic character of a protein. Journal of Molecular Biology 1982;157(1):105–132. doi:10.1016/0022-2836(82)90515-0
6. Meija J, Coplen TB, Berglund M, Brand WA, De Bièvre P, Gröning M, et al. Isotopic compositions of the elements 2013 (IUPAC Technical Report). Pure and Applied Chemistry 2016;88(3):293–306. doi:10.1515/pac-2015-0503
7. Roepstorff P, Fohlman J. Letter to the editors: proposal for a common nomenclature for sequence ions in mass spectra of peptides. Biomedical Mass Spectrometry 1984;11(11):601. doi:10.1002/bms.1200111109
8. Biemann K. Contributions of mass spectrometry to peptide and protein structure. Biomedical and Environmental Mass Spectrometry 1988;16(1–12):99–111. doi:10.1002/bms.1200160119
9. Geiger T, Clarke S. Deamidation, isomerization, and racemization at asparaginyl and aspartyl residues in peptides. Succinimide-linked reactions that contribute to protein degradation. Journal of Biological Chemistry 1987;262(2):785–794. doi:10.1016/S0021-9258(19)75855-4
10. Manning MC, Chou DK, Murphy BM, Payne RW, Katayama DS. Stability of protein pharmaceuticals: an update. Pharmaceutical Research 2010;27(4):544–575. doi:10.1007/s11095-009-0045-6
11. D'Hondt M, Bracke N, Taevernier L, Gevaert B, Verbeke F, Wynendaele E, et al. Related impurities in peptide medicines. Journal of Pharmaceutical and Biomedical Analysis 2014;101:2–30. doi:10.1016/j.jpba.2014.06.012

Cosmic Peptides. (2026, October 25). Melittin: peptide reference entry. Cosmic Peptides Research Library. Retrieved October 26, 2026, from https://cosmicpeptides.com/research/peptides/melittin

@misc{cosmicpeptides_research_peptides_melittin,
  author       = {{Cosmic Peptides}},
  title        = {Melittin: peptide reference entry},
  howpublished = {Cosmic Peptides Research Library},
  year         = {2026},
  month        = oct,
  url          = {https://cosmicpeptides.com/research/peptides/melittin},
  urldate      = {2026-10-26},
  note         = {Last reviewed 2026-10-25}
}

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TI  - Melittin: peptide reference entry
T2  - Cosmic Peptides Research Library
PB  - Cosmic Peptides
PY  - 2026
DA  - 2026/10/25
UR  - https://cosmicpeptides.com/research/peptides/melittin
Y2  - 2026/10/26
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