Adipotide

What Adipotide is, structurally

Adipotide is a chimeric peptidomimetic rather than a straightforward peptide. Two distinct domains are joined by a glycine-glycine linker, and they are built on different chemistry from each other.

The first domain, CKGGRAKDC, is nine residues in the ordinary L-configuration, flanked by a cysteine at each end. The second, written (KLAKLAK)2, is a fourteen-residue repeat in which the residues are D-amino acids, the mirror-image stereochemistry of the natural series. That is the most unusual thing about this molecule. D-residues invert the backbone rather than modify it, and a chain built from them is not a substrate for the enzymes that process ordinary peptides.

Composition is strongly basic. The repeat domain is lysine-rich and the first adds further lysine and an arginine against a single aspartate, so the molecule carries a substantial net positive charge and is highly water soluble. No quantitative figure is quoted here. There is no aromatic residue anywhere in either domain, which determines how purity is measured.

The two sulfur atoms are the interesting part, and the formula settles a question the sequence notation leaves open. Two cysteines can exist either as free thiols or joined as an intramolecular disulfide, and those two states differ by exactly two hydrogens. The supplied formula is C111H206N36O28S2. The disulfide-closed form would be C111H204N36O28S2 at 2555.19. The formula on file is therefore the reduced, open form carrying two free thiols, not a cyclised one. The sequence, though, is conventionally written as though the cysteines were paired, so notation and formula disagree. The formula is the specification and this page follows it.

Reconstitution and handling

Sterile water is the default solvent, and with no metal centre present PBS or an appropriate assay buffer are also reasonable. Add diluent down the inside wall of the vial, swirl gently, and let the solution clarify.

One caution follows from the free thiols. Thiol oxidation is base-catalysed, so a solution held alkaline will close the disulfide or dimerise faster than one near neutral. Prepare fresh, keep the pH near neutral, and limit headspace.

Adsorption is worth allowing for at low concentration, and low-protein-binding tubes reduce it. This molecule is strongly cationic, so negatively charged surfaces such as untreated glass are the likelier route rather than polypropylene.

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. Reconstituted, hold at 2 to 8 degrees C, or aliquot and freeze rather than thawing repeatedly.

The weak point is the pair of free thiols. They can close intramolecularly to the disulfide, losing two hydrogens, or react between molecules to give a dimer at roughly twice the mass. Both are oxidation, both are accelerated by air, alkaline pH and trace metals, and both change what is in the vial rather than merely degrading it.

The D-amino acid domain contributes stability rather than liability, being no substrate for ordinary proteolysis. With no methionine, tryptophan, asparagine or glutamine anywhere, oxidation at sulfur is the only significant route available.

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

How Adipotide is tested

Reversed-phase HPLC establishes chromatographic purity as area percent. With no aromatic residue in either domain, there is no 280 nm absorbance and detection sits in the low UV near 214 nm.

Area percent is a chromatographic measure, not peptide content by weight. Solid-phase synthesis yields a salt, commonly trifluoroacetate or acetate, and on a molecule this basic the counter-ion load is proportionally high, since every lysine is a site for it. Residual trifluoroacetate and deletion sequences are the classes to resolve.

Mass spectrometry does more than confirm identity here: it reads the thiol state directly. Reduced and disulfide-closed forms differ by two mass units, 2557.21 against 2555.19, and a disulfide-linked dimer appears near 5112, so one spectrum distinguishes all three. Ellman's reagent gives the same answer quantitatively, by counting free sulfhydryls.

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

Handling FAQ

Is this supplied with the cysteines paired or free? The formula on file says free. C111H206N36O28S2 is the reduced form; a closed disulfide would be C111H204N36O28S2 and two mass units lighter. The sequence notation is conventionally written as though the pair were closed, so the two disagree. Mass spectrometry or Ellman's assay settles it on actual material.

Why does alkaline pH matter more than usual? Because thiol oxidation is base-catalysed. The deprotonated thiolate oxidises far more readily than the neutral thiol, so a solution held above neutral pH closes the disulfide or dimerises faster than the same material near neutral.

Full specifications for Adipotide.