PE-22-28

What PE-22-28 is, structurally

PE-22-28 is a peptide of seven residues, a short fragment of a longer peptide, spadin, identified from how that chain is broken down. Spadin is seventeen residues; PE-22-28 is seven. They are different substances with different masses, and only the fragment is in the vial.

Two specification fields are empty at source, and both can be filled from the public record. The registry entry for this CAS, not the product database, names the chain glycyl-valyl-seryl-tryptophyl-glycyl-leucyl-arginine, that is Gly-Val-Ser-Trp-Gly-Leu-Arg, and gives C35H55N11O9, which computes to 773.89. That matches the page's approximate 773.9, so the approximation sign looks like caution rather than real uncertainty. One check needs no external source: 773.9 across seven residues is 110.6 each, the ordinary average residue mass.

The composition is lopsided. Of eleven nitrogens, seven are backbone amides, leaving four on side chains, one indole nitrogen from the tryptophan and three from the arginine guanidine. Of nine oxygens, seven are backbone carbonyls and one the C-terminal acid's extra hydroxyl, leaving only the serine hydroxyl. One basic side chain, no acidic side chain at all.

Three groups ionise: the N-terminal amine, the C-terminal carboxylate, and the arginine guanidinium, which stays protonated throughout, so net charge near neutrality is about plus one and the isoelectric point sits in the basic region. Valine, leucine and the indole set hydrophobic surface against that, making this a small amphipathic peptide rather than a freely soluble one.

No sulfur appears in the formula, which closes disulfide, thiol and methionine-sulfoxide chemistry entirely, and no proline, so the backbone carries none of the stiffness or slow isomerism proline brings.

Reconstitution and handling

Sterile water is the default solvent. Where a vial is slow to clear, a trace of dilute acetic acid does more than adding water: mildly acidic conditions aid a basic peptide, the reverse of what helps an acidic one.

Add diluent down the inside wall, swirl gently, and let it clarify. Vortexing produces foam, not faster dissolution.

Neutral buffers such as PBS also suit it and stay clear of the basic pH at which it is least soluble. With this much hydrophobic surface it adsorbs onto polypropylene more readily than a purely polar peptide, so low-protein-binding tubes are worth using at low concentrations.

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 reach room temperature before opening so moisture does not condense onto the solid. Reconstituted, hold at 2 to 8 degrees C briefly, or aliquot and freeze rather than repeatedly thawing one vial.

The degradation profile is narrower than most peptides. With no asparagine or glutamine, the deamidation route that usually dominates peptide ageing is absent, and with no aspartate there is no succinimide or isoaspartate rearrangement either.

That leaves one weak point. The tryptophan indole oxidises readily and is the most photosensitive group a peptide commonly carries, so light protection here is a genuine requirement, not a default precaution. Keep solutions from peroxide-bearing solvents and oxidising buffer additives.

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

How PE-22-28 is tested

Reversed-phase HPLC establishes chromatographic purity as area percent, and this molecule suits it. Tryptophan, leucine and valine give real retention on a standard C18 column, so early elution near the void volume is not expected. Without proline there is no slow cis-trans isomerism, so a split peak means a real impurity, not a conformational artefact.

The single tryptophan absorbs at 280 nm as well as the 214 nm backbone band, and 280 nm is much the more selective, since impurities lacking the indole do not appear there.

Area percent is a chromatographic measure, not peptide content by weight: an arginine-bearing peptide is isolated as a salt, and its trifluoroacetate or acetate counter-ion adds to the weighed mass.

Mass spectrometry confirms identity. On the registry formula the average mass is 773.89 and the monoisotopic 773.42, half a unit apart, so a nominal reading can look half a unit wrong through convention alone. Establish the reporting basis first. Electrospray should give the protonated ion near 774.4 and, given the arginine, a doubly charged species near 387.7. The impurity worth watching for is oxidised tryptophan, sixteen units above the parent.

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

Handling FAQ

The product page gives the weight as approximately 773.9. Is the exact value known? The registry record for this CAS gives C35H55N11O9, which computes to 773.89, agreeing with the page's approximation to within a hundredth. The uncertainty looks presentational rather than chemical, though the formula is not held in the database.

Does this peptide need protecting from light in solution as well as dry? Yes, and more so. The tryptophan indole is the photosensitive group, and it is far more exposed in solution than in a dry cake. Use amber vials or foil for anything held longer than a session.

Full specifications for PE-22-28.