Amyloid-β (1–40)

A 40-residue peptide (human sequence) with a charged N-terminal region and a hydrophobic C-terminal region; prone to aggregation in solution. 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-Asp-Ala-Glu-Phe-Arg-His-Asp-Ser-Gly-Tyr-Glu-Val-His-His-Gln-Lys-Leu-Val-Phe-Phe-Ala-Glu-Asp-Val-Gly-Ser-Asn-Lys-Gly-Ala-Ile-Ile-Gly-Leu-Met-Val-Gly-Gly-Val-Val-OH

One-letter code: DAEFRHDSGY EVHHQKLVFF AEDVGSNKGA IIGLMVGGVV

• 40 residues
• N-terminus: free amine
• C-terminus: free acid

Calculated properties

Calculated from the structure

Property	Value
Molecular formula	C194H295N53O58S
CAS Registry Number	131438-79-4
Average molecular weight	4,329.87 g/mol
Monoisotopic mass	4,327.1484 Da
Net charge at pH 7	-2.3
Isoelectric point	5.43
Molar absorption coefficient, 280 nm	1,490 M−1 cm−1
Hydropathy (GRAVY)	0.06

Net charge across the pH range

pH 2	pH 4	pH 6	pH 7	pH 8	pH 10	pH 12
6.9	3.3	-0.7	-2.3	-3.1	-4.7	-7.1

Composition: Gly 6, Val 6, Ala 3, Asp 3, Glu 3, His 3, Phe 3, Ile 2, Leu 2, Lys 2, Ser 2, Arg 1, Asn 1, Gln 1, Met 1, Tyr 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]+	4,328.1557
[M+2H]2+	2,164.5815
[M+3H]3+	1,443.3901
[M+4H]4+	1,082.7944
[M+5H]5+	866.4370
[M+6H]6+	722.1987
[M+Na]+	4,350.1376
[M+K]+	4,366.1116

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+2. A spectrum read at its tallest peak, or a deconvoluted mass from it, sits about 2.01 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+6H]6+
M (monoisotopic)	34.2	4,327.1484	4,328.1557	2,164.5815	1,443.3901	1,082.7944	866.4370	722.1987
M+1	80.5	4,328.1513	4,329.1586	2,165.0829	1,443.7244	1,083.0451	866.6375	722.3658
M+2	100.0	4,329.1540	4,330.1612	2,165.5843	1,444.0586	1,083.2958	866.8381	722.5329
M+3	86.7	4,330.1565	4,331.1637	2,166.0855	1,444.3928	1,083.5464	867.0386	722.7000
M+4	58.6	4,331.1589	4,332.1661	2,166.5867	1,444.7269	1,083.7970	867.2390	722.8671
M+5	32.8	4,332.1612	4,333.1685	2,167.0879	1,445.0610	1,084.0476	867.4395	723.0341
M+6	15.8	4,333.1635	4,334.1707	2,167.5890	1,445.3951	1,084.2981	867.6400	723.2012
M+7	6.7	4,334.1657	4,335.1730	2,168.0901	1,445.7292	1,084.5487	867.8404	723.3682
M+8	2.5	4,335.1679	4,336.1752	2,168.5912	1,446.0633	1,084.7993	868.0409	723.5353
M+9	0.9	4,336.1702	4,337.1774	2,169.0924	1,446.3973	1,085.0498	868.2413	723.7023

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	116.0342	58.5207	Asp	—	—	40
2	187.0713	94.0393	Ala	4,213.1288	2,107.0680	39
3	316.1139	158.5606	Glu	4,142.0916	2,071.5495	38
4	463.1823	232.0948	Phe	4,013.0491	2,007.0282	37
5	619.2835	310.1454	Arg	3,865.9806	1,933.4940	36
6	756.3424	378.6748	His	3,709.8795	1,855.4434	35
7	871.3693	436.1883	Asp	3,572.8206	1,786.9139	34
8	958.4013	479.7043	Ser	3,457.7937	1,729.4005	33
9	1,015.4228	508.2150	Gly	3,370.7616	1,685.8845	32
10	1,178.4861	589.7467	Tyr	3,313.7402	1,657.3737	31
11	1,307.5287	654.2680	Glu	3,150.6769	1,575.8421	30
12	1,406.5971	703.8022	Val	3,021.6343	1,511.3208	29
13	1,543.6560	772.3317	His	2,922.5658	1,461.7866	28
14	1,680.7150	840.8611	His	2,785.5069	1,393.2571	27
15	1,808.7735	904.8904	Gln	2,648.4480	1,324.7276	26
16	1,936.8685	968.9379	Lys	2,520.3894	1,260.6984	25
17	2,049.9526	1,025.4799	Leu	2,392.2945	1,196.6509	24
18	2,149.0210	1,075.0141	Val	2,279.2104	1,140.1088	23
19	2,296.0894	1,148.5483	Phe	2,180.1420	1,090.5746	22
20	2,443.1578	1,222.0825	Phe	2,033.0736	1,017.0404	21
21	2,514.1949	1,257.6011	Ala	1,886.0052	943.5062	20
22	2,643.2375	1,322.1224	Glu	1,814.9681	907.9877	19
23	2,758.2645	1,379.6359	Asp	1,685.9255	843.4664	18
24	2,857.3329	1,429.1701	Val	1,570.8985	785.9529	17
25	2,914.3543	1,457.6808	Gly	1,471.8301	736.4187	16
26	3,001.3864	1,501.1968	Ser	1,414.8086	707.9080	15
27	3,115.4293	1,558.2183	Asn	1,327.7766	664.3919	14
28	3,243.5243	1,622.2658	Lys	1,213.7337	607.3705	13
29	3,300.5457	1,650.7765	Gly	1,085.6387	543.3230	12
30	3,371.5828	1,686.2951	Ala	1,028.6173	514.8123	11
31	3,484.6669	1,742.8371	Ile	957.5802	479.2937	10
32	3,597.7510	1,799.3791	Ile	844.4961	422.7517	9
33	3,654.7724	1,827.8898	Gly	731.4120	366.2096	8
34	3,767.8565	1,884.4319	Leu	674.3906	337.6989	7
35	3,898.8970	1,949.9521	Met	561.3065	281.1569	6
36	3,997.9654	1,999.4863	Val	430.2660	215.6366	5
37	4,054.9868	2,027.9971	Gly	331.1976	166.1024	4
38	4,112.0083	2,056.5078	Gly	274.1761	137.5917	3
39	4,211.0767	2,106.0420	Val	217.1547	109.0810	2
40	—	—	Val	118.0863	59.5468	1

Immonium ions (low-mass markers of the residues present): Gly 30.0338, Ala 44.0495, Ser 60.0444, Val 72.0808, Leu 86.0964, Ile 86.0964, Asn 87.0553, Asp 88.0393, Gln 101.0709, Lys 101.1073, Glu 102.0550, Met 104.0528, His 110.0713, Phe 120.0808, Arg 129.1135, Tyr 136.0757.

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
Methionine oxidation	+15.995 Da per oxidized residue	Methionine at position 35 can oxidize to the sulfoxide, which usually elutes slightly earlier in reversed-phase HPLC.
Asparagine deamidation	+0.984 Da	Asparagine at position 27 can deamidate to aspartic or isoaspartic acid through a succinimide intermediate. Moisture, higher pH and warmth speed it up.
Glutamine deamidation	+0.984 Da	Glutamine at position 15 can also deamidate, much more slowly than asparagine.
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). Amyloid-β (1–40): peptide reference entry. Cosmic Peptides Research Library. Retrieved October 26, 2026, from https://cosmicpeptides.com/research/peptides/amyloid-beta-1-40

@misc{cosmicpeptides_research_peptides_amyloid_beta_1_40,
  author       = {{Cosmic Peptides}},
  title        = {Amyloid-β (1–40): peptide reference entry},
  howpublished = {Cosmic Peptides Research Library},
  year         = {2026},
  month        = oct,
  url          = {https://cosmicpeptides.com/research/peptides/amyloid-beta-1-40},
  urldate      = {2026-10-26},
  note         = {Last reviewed 2026-10-25}
}

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