PNC-27

What PNC-27 is, structurally

PNC-27 is a peptide of thirty-two residues, and the product page describes it as a chimeric construct: a defined span of the p53 protein, residues twelve to twenty-six, joined to a second segment. What either block does belongs on another page. What matters here is that the molecule is one covalent chain, and that the composition of the whole governs how it behaves in a vial.

The formula gives that composition. Of fifty-three nitrogens, thirty-two are backbone amides, leaving twenty-one on side chains. Of forty-four oxygens, thirty-three belong to the backbone, being thirty-two carbonyls plus the terminal acid, leaving eleven. Twenty-one side-chain nitrogens against eleven side-chain oxygens is a markedly nitrogen-rich balance, which on a peptide means abundant basic side chains and very few acidic ones.

The consequence is a strongly basic peptide with a high isoelectric point, carrying substantial net positive charge at neutral pH. That one property drives most of what follows, and it inverts standard advice.

There is one sulfur. One sulfur cannot form an intramolecular disulfide, which requires two, so no internal bridge is possible and no cross-link to reduce or scramble. The formula alone cannot say what the atom is, since a methionine thioether and a free cysteine thiol are equally consistent with it and they behave differently: a thioether oxidises to the sulfoxide and gains sixteen units, while a free thiol can dimerise to roughly twice the molecular weight. The deposited structure for this CAS settles it, showing a methionine thioether and no free thiol. Limiting air exposure is the right precaution under either reading.

Reconstitution and handling

Sterile water is the default solvent. Where a vial dissolves reluctantly, mildly acidic conditions are the correct escalation here rather than the wrong one, because lowering the pH raises the net positive charge on an already basic peptide and increases its solubility. Dilute acetic acid is the conventional choice. On an acidic peptide the same addition would drive the solution toward minimum solubility.

Add diluent slowly down the inside wall of the vial, swirl gently, and let the solution clarify. Vortexing produces foam without dissolving anything faster. No reducing agent is needed, since there is no disulfide for one to act on.

Container choice deserves real attention here. A strongly cationic peptide binds avidly to negatively charged surfaces, and borosilicate glass is exactly such a surface, so glass is a poor default here and low-protein-binding polypropylene the better one. At low working concentration, adsorptive loss on a peptide this cationic can be a large fraction of what was weighed out rather than the trace it would be on a neutral sequence.

This is laboratory preparation chemistry, not dosing, administration, or protocol guidance of any kind.

Storage and stability

Store the lyophilized powder at -20 degrees C, sealed, desiccated and protected from light, and let a cold vial warm before opening so moisture does not condense on the solid. Reconstituted, hold at 2 to 8 degrees C, or aliquot and freeze rather than thawing repeatedly.

Methionine oxidation is the named liability. Air exposure, warmth and light accelerate it, and the product is sixteen units heavier, which mass spectrometry resolves cleanly. A sealed, cold, dark vial is the control.

The low side-chain oxygen count means comparatively few acidic and amide side chains, which limits the deamidation and isomerisation routes without removing them. With no sequence on file, this page will not name residue positions for either.

These are storage conditions for the material, not dosing or administration guidance.

How PNC-27 is tested

Reversed-phase HPLC establishes chromatographic purity as area percent. Retention is the thing to anticipate: a peptide this basic and this highly charged retains poorly on a standard C18 column, so ion-pairing is effectively required rather than optional. Trifluoroacetic acid serves that purpose and sharpens peak shape.

Area percent is a chromatographic measure, not peptide content by weight. Solid-phase synthesis delivers a salt, and on a peptide carrying this much positive charge the counter-ion is a substantial share of the vial contents, usually residual trifluoroacetate.

Mass spectrometry confirms identity against 4031.72. The useful diagnostics are a result sixteen units high, indicating the sulfoxide, and truncated or deletion sequences, which appear as discrete lower masses rather than as a broadened peak.

These describe general methodology, not a claim about any particular batch.

Handling FAQ

Is this the same compound as PNC-28? No, they are separate molecules. PNC-27 carries p53 residues twelve to twenty-six. PNC-28 carries residues seventeen to twenty-six, five residues fewer, on the same second segment. That difference is several hundred mass units, so the two are easy to separate on analysis and are not interchangeable stock.

Why is glass a poor container for a dilute solution of this peptide? Because the peptide is strongly cationic and a borosilicate surface is negatively charged, so the two attract. On a concentrated stock the loss is immaterial. On a dilute working solution it can remove enough material to shift a measured concentration, and low-protein-binding polypropylene avoids most of it.

Full specifications for PNC-27.