How does Selank vs tuftsin LC-MS analytical differentiation start from sequence?
The comparison is structural. Tuftsin is the tetrapeptide Thr-Lys-Pro-Arg (TKPR), handled as the free acid unless the lot record declares an amide. Selank is the heptapeptide formed by extending that motif with Pro-Gly-Pro, giving Thr-Lys-Pro-Arg-Pro-Gly-Pro (TKPRPGP), again as the free acid unless amidation is stated. The shared prefix causes the naming mix-up. Chain length, elemental formula and monoisotopic mass are what LC-MS has to confirm. Indexing is consistent on the analogue relationship and inconsistent on spelling, so the batch file needs a controlled vocabulary. A 2022 paper indexes Selank as a peptide analog of tuftsin (PMID:36322304). A 2019 paper uses analogue (PMID:31625062). A 2017 review places tuftsin with its analogs, which is the right context for refusing to treat parent and analogue as one catalogue entry (PMID:28745220). Records from 2014 and 2011 likewise call Selank a tuftsin analog (PMID:24291245; PMID:21609736). Those papers are not LC-MS methods. Transliteration is a separate control. Taftsin and taftsin appear in Russian-language titles for the tetrapeptide family (PMID:12154572; PMID:8704608). Copying Taftsin into an English mass field without a translation check can attach the wrong formula to the vial. TP-7 is indexed as a tuftsin analogue in separate records (PMID:16963804; PMID:8704608). A line that bundles tuftsin analogues does not authorise equating TP-7 with Selank or with tuftsin. Equivalence is an intact-mass and fragment-ion conclusion, not a synonym conclusion. Before integration, the identity block should list common name, three-letter and one-letter sequence, acid or amide terminus, elemental formula, theoretical monoisotopic mass, and the lot identifier matched to the vial, the chromatogram sample name and the mass-spectral file name.
Which monoisotopic masses and charge states separate the two peptides?
For the free-acid forms, the theoretical monoisotopic mass of tuftsin, C21H40N8O6, is 500.3071 Da. Selank, C33H57N11O9, is 751.4341 Da. The difference, 251.1270 Da, equals proline plus glycine plus proline. The intact molecules are not isobaric. A deconvoluted mass near 500.3 Da on a vial labelled Selank, or near 751.4 Da on a vial labelled tuftsin, fails identity before purity is discussed. These figures are calculated for method design. They are not measurements copied from the nomenclature papers cited on this page. Charge state still has to be assigned, because raw m/z values sit closer together than the neutral masses. With a proton mass of 1.0073 Da, tuftsin gives m/z 501.3144, 251.1608 and 167.7763 for the 1+, 2+ and 3+ ions. Selank gives m/z 752.4414, 376.7243 and 251.4853. Two traps follow. Do not compare tuftsin [M+2H]2+ at m/z 251.1608 with the neutral Pro-Gly-Pro increment of 251.1270 Da without deconvolution. Selank [M+3H]3+ at m/z 251.4853 and tuftsin [M+2H]2+ at m/z 251.1608 both lie near nominal m/z 251. Isotope spacing, about 0.50 m/z for 2+ and about 0.33 m/z for 3+, separates them. The record should state observed m/z, assigned charge and deconvoluted monoisotopic mass. Both peptides carry the same ionisable groups in positive electrospray under acidic conditions: the N-terminus, lysine and arginine. The extension adds no basic site, so a similar charge envelope is expected and is not identity. A trifluoroacetate adduct of 113.9929 Da on tuftsin does not coincide with Selank, but an unassigned adduct can be mis-filed as an unknown related substance. State the mass-accuracy window actually used for the lot.
Which tandem-MS y ions locate the Pro-Gly-Pro extension?
Intact mass separates the free-acid heptapeptide from the free-acid tetrapeptide, but it does not prove residue order. A sequence isomer of identical composition would still weigh 751.4341 Da. Tandem MS is the sequence check. For peptides this short, coverage is realistic if the precursor is isolated and product ions are matched to a calculated list rather than read by eye. Singly charged y ions locate the C-terminus. Tuftsin ends in arginine, so y1 is m/z 175.119. Selank ends in proline, so y1 is m/z 116.071, y2 (Gly-Pro) is m/z 173.092 and y3 (Pro-Gly-Pro) is m/z 270.145. A dominant m/z 175.119 without the proline series supports the tetrapeptide. The pair m/z 116.071 and m/z 270.145 supports the extension. These values use residue masses plus 19.0178 Da. They are theoretical design figures, not published spectra, and they still sit inside the laboratory fragment-mass tolerance. The N-terminal series is shared. A b2 ion for Thr-Lys falls near m/z 230.150, and a b4 ion for Thr-Lys-Pro-Arg falls near m/z 483.304. On tuftsin that b4 ion is also [M+H-H2O]+. On Selank it shows only that the prefix is intact. Reporting b4 without C-terminal y ions leaves the extension unproven. Proline directs cleavage to its N-terminal side, so the Arg-Pro bond in Selank can give an intense y3. Intensity helps only after the m/z match. Internal fragments in proline-rich spectra can land near a diagnostic mass and should stay unexplained if they do not fit the full list. A paper that treats Selank and its fragments as distinct chemical species is a reminder to assign those ions, not a substitute for a lot-specific product-ion spectrum (PMID:21786679).
When is a Selank truncation isobaric with tuftsin?
The serious overlap is not between the intact peptides. It is between tuftsin and a Selank deletion that removes Pro-Gly-Pro entirely. If what remains is free-acid Thr-Lys-Pro-Arg, composition and monoisotopic mass match tuftsin at 500.3071 Da. In a related-substances run it is a tetrapeptide impurity; in a mislabelled vial it may be the main component. The lot record has to state which question was asked. Other deletions should not be forced into the tuftsin row. Loss of one C-terminal proline leaves Thr-Lys-Pro-Arg-Pro-Gly at 654.3813 Da. Loss of Gly-Pro leaves 597.3598 Da. A single-residue substitution will not match 500.3071 Da either. Only des-Pro-Gly-Pro, or an independent TKPR synthesis, matches tuftsin. Processing that extracts only the Selank mass will miss that impurity. The extracted-ion list should include 751.4341 Da, 500.3071 Da and the single-residue deletion masses the method can detect. Co-elution is the same error in the time domain. On a short gradient a minor tetrapeptide can sit near the heptapeptide, particularly if thresholds are raised to tidy the purity percentage. Area percent at 214 nm does not identify the minor peak, and a diode-array peak-purity flag does not supply sequence. Orthogonal evidence is a resolved related-substances chromatogram or an extracted-ion trace at the tuftsin m/z across the Selank peak, with charge state confirmed. A positive trace should be reported with relative retention time and assigned mass, not merged into the main peak. Short-chain species are already part of how this series is indexed. One indexed title treats Selank and its fragments as distinct inputs (PMID:21786679). Another places Selank beside short peptides of Taftsin derivatives (PMID:12154572). Both support keeping those masses on the theoretical list. A Selank certificate that never looks for 500.3071 Da has not completed Selank vs tuftsin LC-MS analytical differentiation.
Which reversed-phase HPLC records make the mass assignment usable?
Mass spectrometry assigns the ion. Reversed-phase chromatography must show that the assigned ion is the integrated peak, and that a tetrapeptide is not sitting in the baseline. A working expectation, to be tested with reference materials rather than assumed, is that the heptapeptide retains later than the tetrapeptide on C18 in an acidic acetonitrile gradient. Chain length is not a specification. Ion-pair strength and gradient slope can compress retention, and a steep gradient can look resolved on a screenshot while the resolution factor is still poor. The certificate should report column, mobile phase, gradient, flow, wavelength and measured retention times. Neither sequence contains Tyr, Trp or Phe, so 280 nm will not confirm identity. The peptide bond is monitored near 214 nm. Area percent at 214 nm is a purity estimate under stated integration rules. It is not an assay and it is not a mass. The acid is a compromise. Trifluoroacetic acid often sharpens peaks for these basic peptides and can separate deletions, but it suppresses electrospray and forms adducts. Formic acid is usually kinder to the mass spectrometer and harsher on peak shape. Retention order from one acid cannot be pasted onto the other without a bridging injection. System suitability should include resolution between a heptapeptide and a tetrapeptide reference, or between the main peak and the nearest significant related substance, plus a blank showing the m/z channels are free of carry-over. These short basic peptides can adsorb to some plastics and untreated glass, so the record should name vessel, diluent and the interval between dissolution and injection. The analogue papers do not supply these controls. They only document the naming relationship the controls protect (PMID:28745220).
What should an Australian research-lot file show before names are accepted?
The comparison is finished only when a laboratory can replay it against one vial. The identity set is declared sequence and terminus; theoretical formula and monoisotopic mass; observed m/z, charge and deconvoluted mass; fragment ions that distinguish arginine y1 from proline y1; a search at the other peptide mass; HPLC method fields and retention time; and lot concordance across label, certificate header, chromatogram sample name and spectral file. Miss any one field and the file supports a name, not a differentiation. Keep purity in separate columns. Area percent, integration threshold and unidentified peaks do not rescue a wrong mass. Net peptide content, where reported, is not chromatographic purity: counter-ion and moisture add to vial mass without an ultraviolet peak. Australian context sits in the same file as traceability, not as a use instruction. Material released from local stock can be tied to a batch record before dispatch, and tracked dispatch preserves the link between the order and the lot sent. Logistics do not change acceptance criteria. They do make a mismatch queryable, for example a chromatogram sample name that differs from the vial lot, while the consignment record still identifies the package. The certificate is an analytical record for research use. It is not a clinical authorisation and it is not evidence of any effect. Catalogue strings remain unverified until that file exists. Taftsin, tuftsin analogue and TP-7 are indexing labels in the literature, not analytical results (PMID:8704608; PMID:16963804; PMID:12154572). A family review is a reason to expect several sequences under one heading, not a reason to accept any sequence untested (PMID:28745220).
Frequently asked questions
Is Selank the same molecule as tuftsin?
No. Indexed literature describes Selank as a peptide analogue of tuftsin, not as a synonym (PMID:36322304; PMID:31625062). The tetrapeptide is Thr-Lys-Pro-Arg. The heptapeptide used for this comparison is Thr-Lys-Pro-Arg-Pro-Gly-Pro. They share an N-terminal motif and differ by Pro-Gly-Pro, 251.1270 Da. A trade name or a family label does not establish equivalence.
Which m/z values are easy to confuse before deconvolution?
Tuftsin [M+2H]2+ is m/z 251.1608 and Selank [M+3H]3+ is m/z 251.4853. Both sit near nominal m/z 251. Isotope spacing, about 0.50 m/z for a 2+ ion and about 0.33 m/z for a 3+ ion, separates them. The neutral Pro-Gly-Pro increment, 251.1270 Da, is a mass difference, not an ion. Report observed m/z, charge and deconvoluted monoisotopic mass together.
Why do Taftsin and TP-7 complicate a certificate?
Russian-language records transliterate the tetrapeptide family as Taftsin or taftsin (PMID:12154572; PMID:8704608). TP-7 is indexed separately as a tuftsin analogue (PMID:16963804). None of those strings is an observed mass. Copying a transliteration into the theoretical-mass field can attach the wrong formula to a vial. Confirm sequence and intact mass before treating any catalogue synonym as Selank or as tuftsin.
Does an HPLC purity percentage differentiate the two peptides?
No. Area percent near 214 nm estimates chromatographic purity under the stated integration rules. Tuftsin and Selank both lack aromatic residues, so 280 nm does not identify either sequence. A minor tetrapeptide can sit near the heptapeptide on a short gradient. Differentiation needs retention time plus an assigned mass, and a deliberate check for a 500.3071 Da species in a Selank lot.
What related-substance mass is the priority check in a Selank lot?
The priority check is 500.3071 Da, the free-acid mass of Thr-Lys-Pro-Arg. That species is isobaric with tuftsin if the Pro-Gly-Pro extension is absent. Single-proline loss at 654.3813 Da and Gly-Pro loss at 597.3598 Da are different impurities and should be listed separately. Extracted-ion processing that looks only for 751.4341 Da will not detect the tetrapeptide.
How should an Australian laboratory file the comparison?
Match one lot number across the vial label, certificate header, chromatogram sample name and spectral file. Record sequence, terminus, theoretical mass, observed m/z, charge, deconvoluted mass and the C-terminal fragment used to distinguish proline from arginine. Keep purity and net content in separate fields. Local stock and tracked dispatch support traceability. They do not change acceptance criteria or authorise any non-research use.
References
- PMID:36322304 — Selank, a Peptide Analog of Tuftsin, Attenuates Aversive Signs of Morphine Withdrawal in Rats — Bull Exp Biol Med — 2022
- PMID:31625062 — Selank, Peptide Analogue of Tuftsin, Protects Against Ethanol-Induced Memory Impairment by Regulating of BDNF Content in the Hippocampus and Prefrontal Cortex in Rats — Bull Exp Biol Med — 2019
- PMID:28745220 — Tuftsin - Properties and Analogs — Curr Med Chem — 2017
- PMID:24291245 — The temporary dynamics of inflammation-related genes expression under tuftsin analog Selank action — Mol Immunol — 2014
- PMID:21609736 — Expression of inflammation-related genes in mouse spleen under tuftsin analog Selank — Regul Pept — 2011
- PMID:21786679 — [Changes in expression of the genes for chemokines, cytokines, and their receptors in response to selank and its fragments] — Genetika — 2011
- PMID:16963804 — Influence of long-term treatment with tuftsin analogue TP-7 on the anxiety-phobic states and body weight — Pharmacol Rep — 2006
- PMID:12154572 — [Selank and short peptides of Taftsin derivatives in regulation of adaptive behavior of animals in stress] — Ross Fiziol Zh Im I M Sechenova — 2002
- PMID:8704608 — [The characteristics of the anxiolytic action of taftsin and its analog TP-7 on behavior and serotonin metabolism in the brain of rats with chronic deprivation of serotoninergic system activity] — Eksp Klin Farmakol — 1995
Research use only
This article is provided for laboratory research and educational purposes only. Products referenced are not for human or veterinary use. ClaraScience makes no therapeutic, medical, or efficacy claims, and nothing here constitutes medical advice.
