PT-141

A cyclic heptapeptide related to α-melanocyte-stimulating hormone: N-acetylated, with norleucine, D-phenylalanine and a lactam bridge between the Asp and Lys side chains. 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: Ac-Nle-Asp-His-D-Phe-Arg-Trp-Lys-OH

• 7 residues
• N-terminus: N-acetyl
• C-terminus: free acid
• a side-chain lactam bridge
• 1 D-residue
• non-standard residues: Norleucine

Calculated properties

Calculated from the structure

Property	Value
Molecular formula	C50H68N14O10
CAS Registry Number	189691-06-3
Average molecular weight	1,025.18 g/mol
Monoisotopic mass	1,024.5243 Da
Net charge at pH 7	0.2
Isoelectric point	9.50
Molar absorption coefficient, 280 nm	5,500 M−1 cm−1
Hydropathy (GRAVY)	Not calculated: the scale covers the standard amino acids only

Net charge across the pH range

pH 2	pH 4	pH 6	pH 7	pH 8	pH 10	pH 12
2.0	1.3	0.8	0.2	0.0	0.0	-0.2

Composition: Arg 1, Asp 1, His 1, Lys 1, Nle 1, Phe 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]+	1,025.5316
[M+2H]2+	513.2694
[M+Na]+	1,047.5135
[M+K]+	1,063.4874

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). The monoisotopic peak is the most abundant.

Isotope peaks (relative abundance, most abundant = 100)

Peak	Abundance	Neutral mass	[M+H]+	[M+2H]2+
M (monoisotopic)	100.0	1,024.5243	1,025.5316	513.2694
M+1	60.4	1,025.5271	1,026.5344	513.7708
M+2	20.0	1,026.5298	1,027.5371	514.2722
M+3	4.7	1,027.5325	1,028.5397	514.7735
M+4	0.9	1,028.5350	1,029.5423	515.2748

Fragment ions (MS/MS)

In tandem mass spectrometry, a peptide closed by a lactam bridge does not break into the simple b- and y-ion ladder: a single cleavage inside the ring leaves it in one piece, so ring fragments need two cleavages and are not listed here. Reducing the sample before analysis is the usual way to sequence the linear parts.

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 6 can oxidize, particularly on exposure to light and air.
Stereochemistry	0 Da	1 residue is in the D-configuration by design. An epimer at any position has the same mass, so stereochemical purity is a chromatographic question.
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). PT-141: peptide reference entry. Cosmic Peptides Research Library. Retrieved October 26, 2026, from https://cosmicpeptides.com/research/peptides/pt-141

@misc{cosmicpeptides_research_peptides_pt_141,
  author       = {{Cosmic Peptides}},
  title        = {PT-141: peptide reference entry},
  howpublished = {Cosmic Peptides Research Library},
  year         = {2026},
  month        = oct,
  url          = {https://cosmicpeptides.com/research/peptides/pt-141},
  urldate      = {2026-10-26},
  note         = {Last reviewed 2026-10-25}
}

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PY  - 2026
DA  - 2026/10/25
UR  - https://cosmicpeptides.com/research/peptides/pt-141
Y2  - 2026/10/26
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