AOD-9604

What AOD-9604 is, structurally

AOD-9604 is a synthetic peptide fragment. Its designation, Tyr-hGH(177-191), describes its construction: a fifteen-residue segment corresponding to positions 177 to 191 of a larger protein, with a tyrosine added at the N-terminus. That describes assembly, not function.

The residue sequence is not recorded in the product database, so the observations here come from the molecular formula and the deposited structure rather than a residue list.

The defining feature is a disulfide bridge. The formula carries two sulfur atoms, the minimum needed to close one, and the deposited structure confirms they are joined rather than free, with an explicit S-S bond closing a ring within the chain. So this is not a simple linear peptide: part of it is a closed loop, and the chain is constrained in a way an open sequence is not.

That governs most of the handling. A closed disulfide is stable to air where a free thiol is not, so atmospheric exposure is not the concern here. The opposite is: anything reducing will open the bridge.

Composition is otherwise hydrophilic. Twenty-three nitrogens across sixteen residues means seven side-chain nitrogens beyond the backbone, indicating several basic or amide-bearing residues. The N-terminal tyrosine supplies an aromatic ring and a phenolic hydroxyl. The peptide is water soluble, though no quantitative figure is quoted here.

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 slowly down the vial wall, swirl gently rather than vortexing, and let the solution clarify.

One check is specific to a disulfide peptide and easy to overlook. Do not use a diluent or buffer containing a reducing agent. Dithiothreitol, TCEP and beta-mercaptoethanol all open the bridge, as does a large excess of any free thiol. Reducing agents are a routine addition to peptide buffers, which is what makes this worth stating: the default habit is wrong here.

Adsorption onto plasticware is worth allowing for at low concentration, with low-protein-binding tubes reducing measured loss. A cyclised peptide is more compact than an open chain of the same length, which tends to reduce surface binding somewhat.

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 disulfide, though not the way a free thiol is vulnerable. The bridge is stable to air but not to reduction, nor to scrambling: at alkaline pH disulfides exchange, and with only one bridge in the molecule the practical outcome is intermolecular exchange giving dimers and higher aggregates. Near-neutral pH suppresses it, which is the main reason to avoid alkaline storage.

Nothing else presents a comparable liability. There is no third sulfur to complicate the pairing, and tyrosine oxidises far less readily than methionine or tryptophan.

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

How AOD-9604 is tested

Reversed-phase HPLC establishes chromatographic purity as area percent. The N-terminal tyrosine gives usable absorbance near 280 nm alongside the low-UV amide measurement at 214 nm, so both channels are available.

Area percent is a chromatographic measure rather than peptide content by weight. Solid-phase synthesis delivers a salt, commonly trifluoroacetate or acetate, sitting outside the molecular weight above. Residual trifluoroacetate and deletion sequences are the impurity classes to resolve.

Mass spectrometry confirms identity and, on this compound, reads the disulfide state directly. A closed bridge weighs two mass units less than the same chain with both cysteines reduced, so the intact molecule at 1815.10 and its reduced form near 1817 are distinguishable in a single spectrum. Running a sample with and without a reducing agent makes it unambiguous, since the mass shifts by exactly two on reduction. A disulfide-linked dimer appears near 3628.

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

Handling FAQ

Can a reducing agent be added to the buffer? No. Dithiothreitol, TCEP and beta-mercaptoethanol will open the disulfide bridge, and a large excess of any free thiol does the same. Since reducing agents are a common default addition to peptide buffers, this is worth checking rather than assuming.

How can the disulfide be confirmed as intact? By mass. The closed bridge is two mass units lighter than the reduced chain, so comparing a spectrum with and without a reducing agent gives a definitive answer: the mass should rise by exactly two when the bridge opens.

Full specifications for AOD-9604.