PNC-28

1 Identity

Synthetic linear chimeric peptide, 27 residues, built by direct fusion without a linker: residues 1-10 are the p53 mdm-2-binding-domain fragment 17-26 (Glu-Thr-Phe-Ser-Asp-Leu-Trp-Lys-Leu-Leu) and residues 11-27 are the Antennapedia-derived penetratin membrane-residency sequence (Lys-Lys-Trp-Lys-Met-Arg-Arg-Asn-Gln-Phe-Trp-Val-Lys-Val-Gln-Arg-Gly). All residues proteinogenic and L-configured. One methionine at chimera position 15, three tryptophans, no cysteine, no disulfide, free N-terminal alpha-amine, free-acid C-terminus, no acylation and no non-proteinogenic residue. Five lysines and three arginines make the molecule strongly basic, so it is supplied as a salt and the counterion mass fraction is not negligible. PNC-28 acetate — which one seller catalogs separately as its own item — CAS 392661-17-5. Do not confuse with PNC-27, the sibling chimera built on p53(12-26), which is 522.60 Da heavier.

Sequence

H-Glu-Thr-Phe-Ser-Asp-Leu-Trp-Lys-Leu-Leu-Lys-Lys-Trp-Lys-Met-Arg-Arg-Asn-Gln-Phe-Trp-Val-Lys-Val-Gln-Arg-Gly-OH; one-letter ETFSDLWKLLKKWKMRRNQFWVKVQRG, 27 residues. Free acid at the C-terminal glycine; free alpha-amine at the N-terminal glutamate. The two halves are ETFSDLWKLL (p53 17-26) and KKWKMRRNQFWVKVQRG (penetratin/MRP). Either half alone is a purchasable peptide and each is a different molecule from this one.

Molecular formula

C164H255N47O37S (free base). No sulfur beyond the single Met15 thioether; no halogen; no phosphorus.

Average mass

3509.196 Da (C164H255N47O37S), from the formula on IUPAC 2021 abridged conventional atomic weights (C 12.011, H 1.008, N 14.007, O 15.999, S 32.06). Two sellers publish 3509.14 and 3509.13 for the identical formula; the same formula on the pre-2021 table (C 12.0107, H 1.00794, N 14.0067, O 15.9994, S 32.065) returns 3509.137, which is exactly what those two figures are. Neither is wrong; this catalog standardizes on the 2021 table and states the basis on the face of the mass. The 0.06 Da spread is analytically irrelevant here and is recorded only so that a purchaser matching certificates across suppliers does not treat it as a discrepancy.

Monoisotopic mass

3506.92377 Da neutral free acid; [M+H]+ 3507.93105. Practical charge states for a molecule with eight basic side chains plus the N-terminus: [M+3H]3+ 1169.98187, [M+4H]4+ 877.73822, [M+5H]5+ 702.39203 (monoisotopic). At this mass a plus or minus 5 ppm window on [M+H]+ is plus or minus 0.018 Da, which is not sufficient on its own to exclude a single deamidation; deconvoluted intact mass must therefore be read together with the peptide map, not instead of it.

Salt / variant note

Six confusables, and the arithmetic separates all but one of them. (1) PNC-27, C188H293N53O44S, 4031.799 avg / 4029.20397 mono — the p53(12-26) chimera, 522.60 Da heavier, stocked beside this article under a name differing by one digit; a certificate reading 4031.8 under a PNC-28 label is PNC-27. The two names are routinely interchanged in trade listings, and a listing written against one of them is never carried onto the other across that 522.60 Da difference. (2) The penetratin/MRP half alone, KKWKMRRNQFWVKVQRG, C104H167N35O21S, 2275.764 avg / 2274.27965 mono — 1233.43 Da lighter, and the cheaper of the two halves to synthesize. (3) The p53(17-26) half alone, ETFSDLWKLL, C60H90N12O17, 1251.447 avg / 1250.65469 mono. (4) C-terminal amide, C164H256N48O36S, 3508.212 avg / 3505.93976 mono — 0.98 Da lighter than the free acid and invisible on any nominal-mass instrument; of the sellers checked none states which terminus its lot carries except one, which writes -OH explicitly. (5) Met15 sulfoxide, plus 15.995, C164H255N47O38S, 3525.195 avg / 3522.91869 mono; Met15 sulfone, plus 31.990, C164H255N47O39S, 3541.194 avg. Three tryptophans sit alongside the methionine, so oxidation is the governing degradation class and the plus 15.995 increment is not diagnostic of the methionine alone. (6) Salt state, which is where the real money moves and which no seller declares: at 3:1 acetate the counterion is 4.88 percent w/w of the vial and at 6:1 it is 9.31 percent; at 3:1 trifluoroacetate it is 8.88 percent and at 6:1 it is 16.31 percent. A molecule with eight basic side chains routinely carries several counterion equivalents, so a purchaser buying 20 mg of an undeclared trifluoroacetate may be buying under 17 mg of peptide. One seller sells "PNC-28 acetate" as a separate item from "PNC-28", which is the market conceding that the counterion is a commercial attribute while leaving the stoichiometry unstated.

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, old and concentrated in one collaborating group. The design paper is Kanovsky and colleagues, PNAS 2001, on peptides from the amino-terminal mdm-2-binding domain of p53 designed from conformational analysis; the in-vivo work is Sarantopoulos and colleagues 2006 (PMID 16688716, mouse) and Michl and colleagues 2008 (PMID 18931881, in vitro and mouse), with an AACR 2008 abstract (LB-195) covering both chimeras. The authorship runs through SUNY Downstate, Weill Cornell and Mount Sinai and is largely common across the reports. Not identified: any registered human trial under this name on ClinicalTrials.gov, any independent replication of the in-vivo work by an unrelated laboratory, any modern pharmacokinetic characterization, and any formal toxicology or genotoxicity package. Those are absences in the located literature and not findings about the world. The citation index page carries each primary report with study-type, species and sample-size badges and states the absences in the same typeface as the citations.

4 Storage & specification

Storage

The labeled condition is lyophilized white to off-white powder in amber Type I glass with a bromobutyl stopper, headspace displaced with nitrogen, one desiccant sachet per shipper, stored at -20 degrees C plus or minus 5 degrees C, desiccated, protected from light, headspace re-blanketed after any subdivision. The light and oxygen controls are the specific controls for methionine and tryptophan oxidation on this sequence and the label states that reason so a receiving technician cannot treat them as optional. Vials are equilibrated to room temperature before opening. A highly basic peptide of this size adsorbs to glass at low concentration, so container-closure qualification includes a measured recovery check on the actual vial and stopper rather than an assumption carried from another product. Shipped on dry ice or in a validated shipper holding not more than 8 degrees C for transit up to 96 hours, with a single-use electronic temperature logger in every shipper.

Shelf life

Provisional 24-month retest interval at -20 degrees C plus or minus 5 degrees C, desiccated and light-protected. Provisional is meant literally: the interval is carried only until this company's own stability program reports, with retains from every launch lot pulled at 0, 3, 6, 12, 18, 24 and 36 months at -20 degrees C and a parallel 12-month arm at 2-8 degrees C, assayed by the stability-indicating RP-HPLC method. Because the governing failure mode is oxidative rather than hydrolytic, total oxidized species are trended as a named attribute and the interval is shortened if they exceed 0.3 percent growth per year at the labeled condition; that trigger is written into the protocol rather than left to judgment. Material reaching retest is re-assayed for purity, water and net peptide content and is either re-dated for a further 12 months or destroyed and recorded on the public failed-lot ledger.