DSIP: structure, nomenclature and handling

The sequence is tryptophan–alanine–glycine–glycine–aspartate–alanine–serine–glycine–glutamate, written WAGGDASGE in single-letter code. It is a nonapeptide with a molecular weight of approximately 849 daltons.

The composition is unusual in two respects. Four of the nine residues are glycine — the smallest amino acid, with a hydrogen atom in place of a side chain — which makes the backbone exceptionally flexible; glycine-rich stretches adopt no preferred conformation and behave as genuinely disordered chains. And two residues, the aspartate and the glutamate, carry acidic side chains with no basic residue anywhere to balance them, giving the molecule a distinctly acidic character and a low isoelectric point. That is unusual in this catalogue, where most sequences are net basic.

The tryptophan at position 1 is the only aromatic residue. It gives the peptide measurable absorbance at 280 nanometres, which most short sequences here lack, and it is also the residue most sensitive to light.

The material is catalogued as DSIP and by its explicit sequence, Trp-Ala-Gly-Gly-Asp-Ala-Ser-Gly-Glu. It carries CAS 62568-57-4. As with most short synthetic peptides, it is typically isolated as an acetate salt, which affects the mass weighed out without altering identity.

A phosphorylated variant appears in the literature, carrying a phosphate group on the serine at position 7. That is a distinct compound: the modification adds a defined 80-dalton increment, so the certificate's stated theoretical mass separates the two unambiguously. Listings using the bare acronym for a phosphorylated construct are imprecise in a way the mass resolves.

Mass spectrometry confirms the intact molecular mass near 849 daltons and distinguishes the unmodified peptide from the phosphorylated variant by a wide margin.

High-performance liquid chromatography resolves the main peak from related substances and yields the purity figure — and for this sequence the chromatogram carries information the mass measurement cannot.

The reason is aspartimide formation. Aspartate-containing sequences are prone during synthesis to an internal cyclization in which the side chain closes onto the backbone, forming a five-membered ring. That ring reopens, but it can reopen the wrong way, producing iso-aspartate: the chain rejoined through the side-chain carboxyl instead of the backbone one. The result is a structural isomer with exactly the same molecular mass as the target — completely invisible to mass spectrometry, at any resolution. It is separable chromatographically, usually eluting close to the main peak, which makes this compound a clear illustration of why the two methods are run together rather than either treated as sufficient.

Glycine following aspartate is the most susceptible arrangement; here the aspartate is followed by alanine, which is less prone but not exempt. It remains the related substance worth looking for on the trace.

HEEZ Research supplies DSIP in a single format: a 5 mg lyophilized vial. There is no second strength in the current catalogue, so the format decision that arises with two-size products does not apply here.

The material is supplied as a lyophilized powder. Freeze-drying removes water and leaves the peptide as a solid, markedly more stable than the same peptide in solution, and stable enough at ambient temperature to ship without refrigeration in transit.

Reconstitution converts the dried cake into a working solution, and it is a standard laboratory step rather than a product specification. Which solvent is used, and at what final concentration, is determined by the protocol in force at the receiving facility.

What HEEZ specifies is the contents of the vial: lyophilized DSIP in a single 5 mg format, stated on the label and on the batch certificate of analysis. Where a protocol is expressed in molar rather than mass terms, the additional figure it needs is the molecular weight, which the certificate records for the batch supplied.

The acidic character has a practical consequence at the bench. A peptide is least soluble near its isoelectric point, and for an acidic sequence that point sits low — so mildly acidic media are the wrong choice here, where they suit the basic sequences elsewhere in this catalogue. It is the clearest example in the batch of why solubility behaviour does not generalise across peptides.

Sealed lyophilized DSIP is ambient-stable for the duration of transit, so no cold chain or insulated packaging is required for shipping. On receipt the vial goes to refrigeration and is kept out of direct light.

Reconstituted material is held refrigerated and used within the window the receiving facility's protocols specify, and repeated freeze-thaw cycling is avoided. Solutions are treated as short-lived relative to the lyophilized form.

Two residue-specific notes govern the discipline here. The tryptophan is photosensitive and susceptible to oxidation, so amber vials or foil wrapping during extended handling is standard practice. And the aspartate route described above is not confined to synthesis — the same rearrangement proceeds slowly in solution, faster at alkaline pH, so a peptide that was clean at manufacture can accumulate the isomer while sitting in a tube. Making solutions up as needed is the mitigation.

The certificate records what an independent facility measured for one specific batch. Its value lies in being batch-specific, so the first check is that the lot number on the document matches the vial in hand.

The identity section compares observed molecular mass against a stated theoretical mass near 849 daltons — not the phosphorylated variant 80 daltons heavier. Note the limit of what that check establishes: a correct mass does not exclude the iso-aspartate isomer, because the isomer weighs the same.

The purity figure is the HPLC main-peak area as a percentage of total peak area, and the attached chromatogram is the document that carries the real information for this compound. A peak eluting close to the main peak is the signature to look for, and its size is the practical measure of how well the synthesis avoided the rearrangement.

Peptide content, or net peptide content, is sometimes reported separately. It accounts for counter-ions and residual water, and it is the figure determining how much actual peptide a nominal 5 mg represents.