Livagen

What Livagen is, structurally

Livagen is a tetrapeptide with a free N-terminal amine and a free C-terminal acid.

The formula reconciles exactly. Five nitrogens means four backbone amides plus the lysine's epsilon-amino group, since glutamate, aspartate and alanine carry no side-chain nitrogen. The nine oxygens divide as three backbone carbonyls, two for the terminal acid, and four across the two acidic side chains.

Charge is mixed and modestly negative. Lysine and the free N-terminal amine give two positive charges against glutamate, aspartate and the C-terminal acid. The peptide is highly polar and freely water soluble, though no quantitative figure is quoted here.

The alanine at position four is easy to pass over, a methyl being the smallest side chain any residue other than glycine carries. That is what makes it worth noting. The residue following an aspartate governs how readily it rearranges, and alanine sits mid-range: large enough to obstruct the reaction, small enough not to prevent it. The consequence is set out under storage.

There is no cysteine, no methionine and no aromatic residue anywhere in the sequence, so the formula contains no sulfur and the molecule has no 280 nm chromophore.

Reconstitution and handling

Sterile water is the default solvent, and with no metal centre present PBS or an appropriate assay buffer are equally suitable. Add diluent down the vial wall, swirl gently, and let it stand until clear. Vortexing only introduces foaming on a peptide this short.

Prepare near neutral. The rearrangement described below is fastest in neutral to mildly alkaline solution, and there is no reason to use acid on a peptide that dissolves readily without it.

Adsorption onto plasticware is worth allowing for at low concentration, and low-protein-binding tubes reduce measured loss, though a small mixed-charge peptide has limited affinity for 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.

Composition rules out most degradation immediately. No cysteine means no thiol oxidation, no methionine means no sulfoxide, and no asparagine or glutamine means no deamidation. Oxidation has no part in this molecule's chemistry, so air exposure is not a concern.

One route remains and it is the ordinary one. The aspartate at position three can rearrange to isoaspartate through a succinimide ring, formed when the backbone nitrogen of the following residue attacks the aspartate side chain. Alanine follows, and its backbone nitrogen carries a hydrogen, so the reaction is genuinely available.

Its rate is unremarkable, which is itself the useful observation. A following residue can accelerate this reaction sharply, obstruct it, or close it entirely. Alanine does none of those: its methyl only modestly hinders the closure, and it carries the backbone hydrogen the reaction requires. The rearrangement therefore runs close to baseline, neither unusually fast nor blocked.

The reaction needs water, so the lyophilized solid is largely protected. Cold and near-neutral storage is the practical control.

How Livagen is tested

Reversed-phase HPLC establishes chromatographic purity as area percent. With no aromatic residue there is no absorbance at 280 nm, so detection sits near 214 nm where the amide bond absorbs. The peptide is small and polar and retains weakly on a standard C18 column.

Area percent is a chromatographic measure rather than peptide content by weight. Solid-phase synthesis delivers a salt, commonly trifluoroacetate or acetate, associating with the single basic site, and on a 461 g/mol peptide that counter-ion is a proportionally large share of the vial contents.

Mass spectrometry confirms identity but cannot see this compound's one degradation route. Isoaspartate is isobaric, so a rearranged molecule weighs what the intact one weighs. Chromatography resolves it, and since the two differ in backbone geometry rather than composition, the method must be demonstrated to separate them rather than assumed to.

A deletion product, by contrast, is a large proportional mass change on a four-residue peptide and is straightforward to identify.

Handling FAQ

Does the residue after the aspartate really affect stability? Substantially. Its backbone nitrogen must attack the aspartate side chain, and its side chain must move aside for the ring to close. A residue with no side chain accelerates it, a bulky one slows it, and proline, whose nitrogen carries no hydrogen, prevents it. Alanine sits in the middle.

Is the main degradation route detectable by mass? No. The rearrangement moves the backbone without changing composition, so the molecular weight is identical. Only chromatography, or an assay specific to isoaspartate, will show it.

Full specifications for Livagen.