ACTH 1-39

What ACTH 1-39 is, structurally

ACTH 1-39 is a polypeptide of thirty-nine residues, which its designation states directly. At 4541.10 g/mol it is an order of magnitude heavier than most of this catalogue, and that scale drives much of what follows.

The sequence is not recorded in the product database, so the observations below derive from the molecular formula rather than a residue list.

Two features fall straight out of the formula. Fifty-six nitrogens across thirty-nine residues means thirty-nine backbone amides and seventeen from side chains, so roughly two residues in five carry nitrogen beyond the backbone. That is a basic, amide-rich composition consistent with multiple arginine, lysine and histidine residues, and it is why the molecule is strongly hydrophilic despite its size.

The second is more definite. There is exactly one sulfur atom, and a disulfide bond requires two, so this polypeptide cannot form an internal disulfide bridge and needs no reducing agent. That single sulfur is a methionine thioether rather than a cysteine thiol, which makes it an oxidation site rather than a cross-linking one.

Charge behaviour has a documented consequence here. The isoelectric point is roughly pH 4.65 to 4.80 and the material partly precipitates there. It is otherwise freely soluble in water, cold or hot, which is a reported property rather than an inference. No figure in mg/mL is quoted.

Reconstitution and handling

Sterile water is the default solvent and the right one here. Add it slowly down the inside wall of the vial, swirl gently, and let it stand until it clarifies. Do not vortex: a chain of this length has conformational structure to lose, and shear and foaming drive aggregation far more readily than in a tetrapeptide.

Buffer choice needs a check shorter peptides do not. Because the material partly precipitates near its isoelectric point, an assay buffer between pH 4.6 and 4.9 can drop it out of solution. Confirm the working pH clears that window first.

Adsorption matters more here than for a small peptide. A large polypeptide presents far more binding surface, and losses at low concentration can be substantial. Low-protein-binding tubes are worth using rather than merely considering.

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

Storage and stability

Store the lyophilized solid at -20 degrees C, sealed, desiccated and protected from light, and let a cold vial reach room temperature before opening. Reconstituted, hold at 2 to 8 degrees C for short-term work, or aliquot and freeze for longer storage.

Freeze-thaw discipline matters more here than for short peptides. A tetrapeptide has no folded structure to disrupt; a thirty-nine-residue chain does, and cycling promotes aggregation as well as chemical degradation. Aliquot before the first freeze.

The identifiable weak point is the single sulfur. A methionine thioether oxidises to the sulfoxide on exposure to air, peroxides or trace metals, and with no cysteine present nothing competes for that role. Limiting headspace and air exposure addresses it. A chain this long also carries the usual aspartyl isomerisation and asparaginyl deamidation liabilities, but without the sequence this page will not name positions.

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

How ACTH 1-39 is tested

Reversed-phase HPLC establishes chromatographic purity as area percent. A chain this long almost certainly contains aromatic residues, so 280 nm detection is generally available alongside the 214 nm amide measurement.

One consequence of size runs opposite to the short peptides. On a tetrapeptide a deleted residue is a large proportional mass change and separates easily. On a thirty-nine-residue chain it alters the mass by around two percent and may barely shift retention, so deletion sequences are harder to resolve and the purity figure rests on a more demanding separation.

Area percent remains a chromatographic measure, not peptide content by weight. Solid-phase synthesis delivers a salt, commonly trifluoroacetate or acetate, lying outside the molecular weight above.

Mass spectrometry confirms identity against the expected weight, and the compound-specific signature is oxidation: sulfoxide formation at the single sulfur appears as a satellite sixteen mass units above the molecular ion. On a molecule of 4541 that is a small relative shift needing adequate resolution to see.

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