What monoisotopic mass follows from the BPC-157 residue string?
The identity calculation starts from Gly-Glu-Pro-Pro-Pro-Gly-Lys-Pro-Ala-Asp-Asp-Ala-Gly-Leu-Val (GEPPPGKPADDAGLV). The worksheet should state the assumptions: all-L residues, a free amino terminus, a free C-terminal carboxylic acid, and no covalent modification. Papers that name this gastric pentadecapeptide describe a defined fifteen-residue chain (PMID:23755725; PMID:36551977). They do not replace a measured mass on the lot under review.
Each residue is the amino acid minus water. Three glycines contribute C6H9N3O3, one glutamic acid C5H7NO3, four prolines C20H28N4O4, one lysine C6H12N2O, two alanines C6H10N2O2, two aspartic acids C8H10N2O6, one leucine C6H11NO and one valine C5H9NO. Adding terminal water yields the neutral formula C62H98N16O22. With monoisotopic atomic masses the neutral monoisotopic mass is 1418.7042 daltons. The average mass, from conventional average atomic weights, is about 1419.53 daltons. The gap, near 0.82 daltons, is definitional. It is not evidence of instrument drift. A certificate that prints 1419.5 beside a high-resolution trace should say whether the figure is average mass, a rounded protonated mass-to-charge value, or a mislabelled monoisotopic mass.
C-terminal amidation lowers the neutral mass by 0.9840 daltons, to about 1417.7202 daltons. Near m/z 1419 a 5 parts-per-million window is only about 0.007 daltons wide, so the amide and the free acid cannot be reconciled by calibration. Exact mass does not encode configuration. A D-residue substitution is isobaric with the all-L chain and will pass any exact-mass window. Stereochemical control, where required, belongs in the synthetic record or in a chiral method.
There is no cysteine, so there is no disulphide pair to confirm. There is no methionine and no tryptophan, so a shift of 15.9949 daltons is not a routine residue oxidation of this sequence. A peak at that offset is a different elemental composition, a processing artefact, or a sequence that is not the target pentadecapeptide.
How is the BPC-157 exact mass and isotopic pattern recognised?
Isotopic pattern recognition compares the observed cluster with the distribution predicted for C62H98N16O22 at a stated charge. Singly charged peaks are spaced by about 1.0034 daltons. Doubly charged peaks are spaced by about 0.5017 daltons. Triply charged peaks are spaced by about 0.3345 daltons. If resolution does not separate those peaks, a fit cannot be made.
A first-order M+1 to monoisotopic ratio is carbon count times 0.0107, plus nitrogen count times 0.00364, plus hydrogen count times 0.000115, plus oxygen count times 0.00038. Substituting 62, 16, 98 and 22 gives about 0.74. The monoisotopic peak is therefore still the tallest peak. An M+2 estimate is dominated by two 13C atoms (about 0.22) plus one 18O (about 0.045) and the 13C–15N cross term (about 0.04), giving a ratio near 0.30. These are natural-abundance estimates for method design, not lot limits. Recompute them in isotope-modelling software before writing a tolerance.
Calling the M+1 peak monoisotopic shifts the reported mass by about 1.003 daltons. At m/z 1419 that error is hundreds of parts per million. A tight window rejects it only if the method must report the monoisotopic peak rather than an average mass. Centroiding a partly resolved cluster can pull the value toward the heavier isotopes and bias the result by several parts per million. Check a calibrant of similar mass-to-charge ratio in the same sequence and require its monoisotopic centroid to fall inside the sample window.
The fit must be charge-state aware. A singly charged theoretical envelope will not match a doubly charged cluster, because the spacing differs. A 0.50 dalton spacing is a doubly charged ion, not a singly charged impurity at half the mass. The identity conclusion is the neutral monoisotopic mass after the stated charge is removed, plus a documented isotope-ratio match. In negative mode, acetate or trifluoroacetate adducts add carbon or fluorine and change the M+1 ratio.
Which charge states and adduct ions move the observed mass-to-charge ratio?
Electrospray measures mass-to-charge ratio, not the neutral mass directly. Using a proton mass of 1.007276 daltons, [M+H]+ of the free acid falls at 1419.7115, [M+2H]2+ at 710.3594, and [M+3H]3+ at 473.9087. The deprotonated ion [M−H]− falls at 1417.6969. A certificate that reports 1419.7 without a charge state is ambiguous, because that number sits near both the singly protonated ion and the average neutral mass. The record should print the ion formula, the charge, and the theoretical mass-to-charge ratio used as the target.
Parts-per-million windows scale with mass-to-charge ratio. Five parts per million at 710.359 is about 0.0036 daltons. The same five parts per million at 473.909 is about 0.0024 daltons. A window copied from a singly charged method onto a triply charged trace, without converting units, will be too wide or too tight. State lock-mass or external calibration error in the same units as the acceptance window.
Adducts are the usual reason a correct peptide appears to miss its window. Replacing a proton with sodium raises the ion mass by 21.9819 daltons. Potassium raises it by 37.9559 daltons. On a doubly charged ion those shifts are about 10.991 and 18.978 daltons in mass-to-charge ratio. The trifluoroacetate anion, CF3COO, adds 112.9850 daltons. Neutral trifluoroacetic acid is 113.9929 daltons, so the two figures must not be swapped. Acetate adds 59.0133 daltons as C2H3O2. Identity remains available if subtracting the adduct mass recovers 1418.7042 daltons and the isotope envelope matches the adduct formula. Reporting the adduct as the protonated molecule is an identity error.
Salt form is not the same as an in-spectrum adduct. An acetate or arginate solid can still yield the free-peptide ion once the salt dissociates during ionisation. The peptide monoisotopic mass does not change because acetate or arginine is present as a counter-ion. Gross mass, chromatographic behaviour, and the adduct population can change. A lot record that names an arginate or acetate salt needs a counter-ion result, or a labelled chromatographic comparison, in addition to the peptide exact mass. The peptide ion alone cannot prove which salt was bottled.
How do sequence-related mass defects differ from conformers?
A mass error of a few parts per million and a whole-residue defect are not the same finding. Deletion of glycine lowers the neutral mass by 57.0215 daltons. Deletion of proline lowers it by 97.0528 daltons. Deletion of alanine lowers it by 71.0371 daltons. Those shifts should be reported as related substances or as identity failures against the fifteen-residue target, not folded into a purity percentage.
Aspartimide formation fits this sequence. Two aspartic acid residues sit side by side. Loss of water, forming a succinimide, lowers the mass by 18.0106 daltons. That offset is composition, not calibration. The reverse case is the limit of the method. Isoaspartic acid has the same elemental formula as aspartic acid, so exact mass cannot separate them at any resolution. A lot can match 1418.7042 daltons and still contain an isoaspartate rearrangement. Where that distinction matters, the laboratory needs chromatography that resolves the isomer, or tandem spectra that show the rearrangement, not a tighter window on the intact ion.
Proline conformers cause the other false alarm. Four proline residues can adopt cis and trans peptide bonds. Those species can separate on a reversed-phase column and look like impurities. They do not change the elemental formula, so they share one exact mass and one isotope envelope. A second peak with the same monoisotopic mass is a candidate conformer or isobaric isomer.
N-terminal acetylation adds 42.0106 daltons. A sodium adduct adds 21.9819 daltons. Water loss (18.0106 daltons) and ammonia loss (17.0265 daltons) should be resolved before a related-substance table is signed. This sequence has no asparagine and no glutamine, so a shift of 0.9840 daltons is not deamidation of the target. If that shift is real, the chain is not the specified pentadecapeptide, or the C-terminus has been assigned as the wrong acid or amide form.
Exact mass does not read residue order. Many fifteen-residue sequences are isobaric. Sequence ions, or a peptide-map result, are the orthogonal check. Literature that treats this analyte as one defined pentadecapeptide (PMID:14554208; PMID:21030672; PMID:34380875) is a reason to demand that order, not a reason to skip the measurement.
What should an Australian research COA show before a BPC-157 lot is accepted?
An identity block that a second laboratory can audit is more useful than a single bold number. The certificate, or the attached batch report, should name the free-acid pentadecapeptide, state the theoretical neutral monoisotopic mass of 1418.7042 daltons, state the ion and charge measured, and state the theoretical mass-to-charge ratio. It should report the observed mass-to-charge ratio, the error in parts per million or millidaltons, and the window applied before a pass was assigned. If software reported an average mass, that value must not occupy the monoisotopic field.
Isotope evidence needs its own line. State the resolving power at the measured mass-to-charge ratio, whether isotope peaks were separated, and the observed M+1 to monoisotopic ratio against the theoretical ratio for the assigned formula. For an adduct, recompute the ratio with the adduct atoms included. A match factor is acceptable if the method defines it. Traceability fields stop a correct spectrum being paired with the wrong vial: sample name, lot number, acquisition date, instrument identifier, and method identifier should match the chromatographic header and the label. Record the calibrant and the reviewer sign-off in the same block. If a testing laboratory cites ISO/IEC 17025 or NATA accreditation, the certificate should show that the method sits inside the stated scope.
Acceptance criteria should be written before the error is known. Laboratories commonly document 5 or 10 parts per million on the assigned monoisotopic ion, plus an isotope-ratio tolerance set during method qualification. Widening a window after a miss, without a new method version, is a documentation failure.
For supplier comparison, area-percent purity does not identify the chain. One file may show a monoisotopic error within 3 parts per million and an M+1 ratio near 0.74. Another may show 1419.5 with no charge state and no envelope. On multi-vial lots, state whether every vial was tested or whether a written sampling plan was used. Red flags are a missing mass, a lot number that differs between spectrum and label, and isotope spacing that disagrees with the stated charge. Published names for the pentadecapeptide (PMID:36200148; PMID:31158953) do not certify a vial. An exact-mass pass supports chemical identity for laboratory research. It is not a therapeutic-goods evaluation.
Frequently asked questions
What monoisotopic mass should unmodified BPC-157 match?
For the unmodified free-acid sequence GEPPPGKPADDAGLV, formula C62H98N16O22, the neutral monoisotopic mass is 1418.7042 daltons. The singly protonated ion falls at 1419.7115, the doubly protonated ion at 710.3594, and the triply protonated ion at 473.9087. A certificate should state which of these values was the target. A figure near 1419.5 is usually an average mass, not the monoisotopic mass, and should be labelled as such.
Why do average mass and exact mass differ by about 0.8 daltons?
Average mass uses average atomic weights, so natural 13C, 15N, 2H and 18O are folded into one number near 1419.53 daltons. Monoisotopic mass uses only the lightest stable isotopes and is 1418.7042 daltons for this formula. The gap is about 0.82 daltons. It is not a failed calibration. High-resolution identity tests should quote the monoisotopic value and the charge state. Mixing the two definitions is a common transcription error on research certificates.
Does an acetate or arginate salt change the peptide exact mass?
No. Acetate and arginate are counter-ions. Once the salt dissociates during electrospray ionisation, the peptide ion still has the free-acid monoisotopic mass of 1418.7042 daltons, provided the chain itself is unmodified. What changes is gross mass of the solid, chromatographic behaviour, and sometimes the adduct ions, such as acetate at 59.0133 daltons. Salt identity needs a counter-ion assay or a chromatographic comparison. Peptide exact mass alone cannot prove which salt was bottled.
Can exact mass detect isoaspartate in BPC-157?
No. Isoaspartic acid and aspartic acid share an elemental formula, so they are isobaric. A perfect match to 1418.7042 daltons does not exclude an isoaspartate rearrangement at either aspartic acid site. Aspartimide, by contrast, is not isobaric: loss of water shifts the mass by 18.0106 daltons and should be visible. Separating isoaspartate from aspartate requires chromatography or tandem mass spectrometry, not a tighter parts-per-million window.
What isotope spacing is expected for the doubly charged ion?
About 0.5017 daltons. The 13C minus 12C difference is about 1.0034 daltons, and a doubly charged ion displays that difference at half the spacing. A triply charged ion displays it at about 0.3345 daltons. If the observed spacing does not match the charge written on the certificate, the neutral mass has probably been miscalculated. Pattern fitting must use the theoretical envelope for that charge, not a singly charged template.
References
- PMID:14554208 — Gastric pentadecapeptide BPC 157 accelerates healing of transected rat Achilles tendon and in vitro stimulates tendocytes growth — J Orthop Res — 2003
- PMID:21030672 — The promoting effect of pentadecapeptide BPC 157 on tendon healing involves tendon outgrowth, cell survival, and cell migration — J Appl Physiol (1985) — 2011
- PMID:23755725 — Stable gastric pentadecapeptide BPC 157-NO-system relation — Curr Pharm Des — 2014
- PMID:30915550 — Gastric pentadecapeptide body protection compound BPC 157 and its role in accelerating musculoskeletal soft tissue healing — Cell Tissue Res — 2019
- PMID:31158953 — Stable Gastric Pentadecapeptide BPC 157, Robert's Stomach Cytoprotection/Adaptive Cytoprotection/Organoprotection, and Selye's Stress Coping Response: Progress, Achievements, and the Future — Gut Liver — 2020
- PMID:34267654 — Stable Gastric Pentadecapeptide BPC 157 and Wound Healing — Front Pharmacol — 2021
- PMID:34380875 — Pentadecapeptide BPC 157 and the central nervous system — Neural Regen Res — 2022
- PMID:36200148 — Stable Gastric Pentadecapeptide BPC 157: Prompt Particular Activation of Collateral Pathways — Curr Med Chem — 2023
- PMID:36551977 — Stable Gastric Pentadecapeptide BPC 157 and Striated, Smooth, and Heart Muscle — Biomedicines — 2022
Research use only
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