PTD-DBM

1 Identity

Synthetic chimeric peptide: a cationic cell-penetrating octaarginine segment joined by a tetraglycine linker to a 13-residue motif taken from the human CXXC5 protein sequence. Two cysteines in the C-terminal segment make the redox state a defining part of the identity rather than a detail. Not acylated and not amidated in the material offered, no D-residues and no non-proteinogenic residues. and occasionally written PTD DBM or PTD/DBM. Seller copy files it under a hair-loss research category, which is a marketing category and not a name. No CAS Registry Number is in circulation under any of these names. Do not treat "DBM" alone as a synonym: the 13-residue motif on its own is a different article at roughly half the mass, and at least one supplier sells short CXXC5-derived fragments separately.

Sequence

H-Arg-Arg-Arg-Arg-Arg-Arg-Arg-Arg-Gly-Gly-Gly-Gly-Arg-Lys-Thr-Gly-His-Gln-Ile-Cys-Lys-Phe-Arg-Lys-Cys-OH (RRRRRRRRGGGGRKTGHQICKFRKC). TWENTY-five residues, all L, free N-terminal alpha-amine, free C-terminal carboxyl, no acylation, no amidation. Architecture: R8 cell-penetrating segment (1-8), GGGG flexible linker (9-12), RKTGHQICKFRKC motif segment (13-25) taken from the CXXC5 sequence. Eleven arginines and three lysines against no acidic residue at all — fourteen basic centers, which governs the chromatography, the counterion load and the storage. Two cysteines, at positions 20 and 25, and the redox state between them is not settled in the market; the two forms are set out in the salt and variant note below.

Molecular formula

C124H225N61O28S2 as the reduced free-dithiol form, and C124H223N61O28S2 as the intramolecularly disulfide-bridged form. Both are currently printed by live sellers under the identical product name, and the formula is therefore incomplete until the supplier declares which one it ships.

Average mass

3082.683 Da for the reduced free-dithiol form (C124H225N61O28S2) and 3080.667 Da for the disulfide-bridged form (C124H223N61O28S2), both on IUPAC 2021 abridged conventional atomic weights. The formula reconstructs exactly from the stated sequence with free termini and reduced cysteines, which is the arithmetic that makes the sequence attribution usable. One seller prints C124H225N61O28S2 and 3082; another prints C124H223N61O28S2 and 3080.7 g/mol. Each is internally consistent with its own formula, and they describe two different molecules 2.016 Da apart.

Monoisotopic mass

3080.7499 Da neutral for the reduced form; [M+H]+ 3081.7572, and in practice the useful ions are the multiply-charged series generated by fourteen basic centers: [M+3H]3+ 1027.9239, [M+4H]4+ 771.1948, [M+5H]5+ 617.1573, [M+6H]6+ 514.4656. Disulfide-bridged form: 3078.7342 neutral, [M+4H]4+ 770.6908, [M+5H]5+ 616.7541. The pair differ by 2.0157 Da on the neutral, which is 0.504 Da at 4+ and 0.403 Da at 5+ — resolvable on any modern instrument but easily lost if the certificate reports a single nominal number without stating the charge state or the deconvolution.

Salt / variant note

Six axes. (1) redox state, which is the live one: reduced C124H225N61O28S2 3082.683 / 3080.7499 against intramolecular disulfide C124H223N61O28S2 3080.667 / 3078.7342, a 2.016 Da difference between two formulas that are simultaneously being printed by two sellers under one product name. A lot can also be a mixture of the two, which no single mass number describes, so the redox question is answered by LC-MS run non-reduced and reduced and not by one reported mass. (2) intermolecular disulfide dimer: two chains bridged, nominally 6159.47 average, a species that a 5+ charge-state assignment can misread as monomer if the deconvolution is not shown. (3) segment articles: the 13-residue motif alone, RKTGHQICKFRKC, C68H117N25O16S2, 1604.963 / 1603.8552; the R8-GGGG segment alone, C56H110N36O13, 1495.735 / 1494.9053. Both are plausible synthesis failures and both are plausible cheap substitutions. (4) delivery-domain substitution, and this is the one that changes the molecule while keeping the name: an HIV-1 TAT-derived transduction domain in place of the octaarginine, YGRKKRRQRRR-GGGG-RKTGHQICKFRKC, C140H245N61O33S2, 3375.014 / 3372.8810, roughly 292 Da heavy. Seller copy for this class often says only "protein transduction domain", which does not specify which one, and that is why the domain is specified here as octaarginine rather than left generic. (5) arginine count: R7 and R9 variants, C118H213N57O27S2 2926.494 / 2924.6488 and C130H237N65O29S2 3238.872 / 3236.8510, one arginine being 156.189 average / 156.1011 monoisotopic — and a deletion of one arginine in an eight-arginine homopolymer block is the single most likely synthesis defect in this molecule, because coupling efficiency falls in polyarginine stretches. (6) oxidation and counterion: cysteine to cysteic acid is plus 47.985 Da per residue; and with fourteen basic centers a trifluoroacetate salt can carry an enormous counterion load — each mole of TFA is 114.023 average, so a heavily TFA-loaded lot can be a third counterion by mass, with a directly corresponding error in any content calculation that ignores it.

2 Class & testing panel

Form

Single article

Testing panel

P1 — panel definition

3 Primary sources & evidence

The index reports the design and provenance of the literature, not a conclusion about effect.

Published literature exists and it is small, academic in origin and concentrated in one group. The primary identifiers: Lee SH et al., "Targeting of CXXC5 by a Competing Peptide Stimulates Hair Regrowth and Wound-Induced Hair Neogenesis", J Invest Dermatol 2017;137(11):2260-2269, PMID 28595998, DOI 10.1016/j.jid.2017.04.038 — primary experimental study, mouse models and cell-based work; and Lee SH et al., "The Dishevelled-binding protein CXXC5 negatively regulates cutaneous wound healing", J Exp Med 2015;212(7):1061-1080, DOI 10.1084/jem.20141601 — primary experimental study characterizing the target protein and the interaction from which the peptide's motif segment is taken. None of the following has been identified: any registered interventional clinical trial of the peptide, any published human study of any design, any independent replication by a laboratory unaffiliated with the originating group, any published pharmacokinetic or toxicology package, and any regulatory review in any jurisdiction. Seller copy is not evidence. The citation index page prints the count by study type at the top, so the size of the base is visible before the first line of text.

4 Storage & specification

Storage

White to off-white lyophilized powder, acetate or trifluoroacetate salt as declared, sealed original container with in-pack desiccant. Store at -20 degrees C plus or minus 5 degrees C, desiccated, protected from light, equilibrated to room temperature before opening. The cysteines are the reason the container is sealed against air as well as water: a reduced lot left open oxidizes toward the bridged form and toward cysteic acid, and both changes are invisible to an area-percent purity figure. 2-8 degrees C is acceptable for transit and for working stock held no longer than 30 days; validated shipper with a temperature logger, and the excursion record attached to the lot file. Not to be stored in solution; where solution work is unavoidable the diluent is degassed and the interval recorded, because thiol oxidation in aqueous solution is measured in hours, not weeks.

Shelf life

Provisional 24 months at -20 degrees C plus or minus 5 degrees C, desiccated and light-protected, assigned by protocol and not measured. It is provisional in the ordinary sense and also in a specific one: no retest interval can be defended until the redox state is fixed, because the reduced and bridged forms have different degradation pathways and only one of them can oxidize. Stability-indicating attributes are free-thiol content, the 2.016 Da bridged species, the plus 47.985 Da cysteic-acid species, the dimer, water content and counterion. Three lots, long-term at -20 degrees C with pull points at 0, 3, 6, 9, 12, 18 and 24 months, accelerated at 25 degrees C and 60 percent RH and at 40 degrees C and 75 percent RH, plus an open-vial air-exposure arm whose only purpose is to characterize the oxidation the sealed container is there to prevent. Shortened on data, never extended without a completed dataset.