MOTS-c

A 16-residue peptide encoded by a short open reading frame within the mitochondrial 12S rRNA gene. 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-Met-Arg-Trp-Gln-Glu-Met-Gly-Tyr-Ile-Phe-Tyr-Pro-Arg-Lys-Leu-Arg-OH

One-letter code: MRWQEMGYIF YPRKLR

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

Calculated properties

Calculated from the structure

Property	Value
Molecular formula	C101H152N28O22S2
CAS Registry Number	1627580-64-6
Average molecular weight	2,174.62 g/mol
Monoisotopic mass	2,173.1077 Da
Net charge at pH 7	3.0
Isoelectric point	10.64
Molar absorption coefficient, 280 nm	8,480 M−1 cm−1
Hydropathy (GRAVY)	-0.94

Net charge across the pH range

pH 2	pH 4	pH 6	pH 7	pH 8	pH 10	pH 12
5.0	3.8	3.0	3.0	2.8	1.0	-1.6

Composition: Arg 3, Met 2, Tyr 2, Gln 1, Glu 1, Gly 1, Ile 1, Leu 1, Lys 1, Phe 1, Pro 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]+	2,174.1150
[M+2H]2+	1,087.5611
[M+3H]3+	725.3765
[M+4H]4+	544.2842
[M+Na]+	2,196.0970
[M+K]+	2,212.0709

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 (monoisotopic)	80.9	2,173.1077	2,174.1150	1,087.5611	725.3765	544.2842
M+1	100.0	2,174.1106	2,175.1178	1,088.0626	725.7108	544.5349
M+2	72.2	2,175.1123	2,176.1196	1,088.5634	726.0447	544.7854
M+3	38.3	2,176.1138	2,177.1210	1,089.0642	726.3785	545.0357
M+4	16.3	2,177.1151	2,178.1224	1,089.5648	726.7123	545.2860
M+5	5.8	2,178.1164	2,179.1236	1,090.0655	727.0461	545.5364
M+6	1.8	2,179.1177	2,180.1249	1,090.5661	727.3798	545.7867

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	132.0478	66.5275	Met	—	—	16
2	288.1489	144.5781	Arg	2,043.0745	1,022.0409	15
3	474.2282	237.6177	Trp	1,886.9734	943.9903	14
4	602.2868	301.6470	Gln	1,700.8941	850.9507	13
5	731.3294	366.1683	Glu	1,572.8355	786.9214	12
6	862.3698	431.6886	Met	1,443.7929	722.4001	11
7	919.3913	460.1993	Gly	1,312.7525	656.8799	10
8	1,082.4546	541.7310	Tyr	1,255.7310	628.3691	9
9	1,195.5387	598.2730	Ile	1,092.6677	546.8375	8
10	1,342.6071	671.8072	Phe	979.5836	490.2954	7
11	1,505.6704	753.3389	Tyr	832.5152	416.7612	6
12	1,602.7232	801.8652	Pro	669.4519	335.2296	5
13	1,758.8243	879.9158	Arg	572.3991	286.7032	4
14	1,886.9193	943.9633	Lys	416.2980	208.6526	3
15	2,000.0033	1,000.5053	Leu	288.2030	144.6051	2
16	—	—	Arg	175.1190	88.0631	1

Immonium ions (low-mass markers of the residues present): Gly 30.0338, Pro 70.0651, Ile 86.0964, Leu 86.0964, Gln 101.0709, Lys 101.1073, Glu 102.0550, Met 104.0528, Phe 120.0808, Arg 129.1135, Tyr 136.0757, 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
Methionine oxidation	+15.995 Da per oxidized residue	Methionine at positions 1 and 6 can oxidize to the sulfoxide, which usually elutes slightly earlier in reversed-phase HPLC.
Tryptophan oxidation	+15.995 or +31.990 Da	Tryptophan at position 3 can oxidize, particularly on exposure to light and air.
Glutamine deamidation	+0.984 Da	Glutamine at position 4 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). MOTS-c: peptide reference entry. Cosmic Peptides Research Library. Retrieved October 26, 2026, from https://cosmicpeptides.com/research/peptides/mots-c

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

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T2  - Cosmic Peptides Research Library
PB  - Cosmic Peptides
PY  - 2026
DA  - 2026/10/25
UR  - https://cosmicpeptides.com/research/peptides/mots-c
Y2  - 2026/10/26
LA  - en
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