VIP (Vasoactive Intestinal Peptide)

What VIP is, structurally

VIP is a peptide of twenty-eight residues carrying a C-terminal amide rather than the free acid most synthetic peptides end in. The product page states the amidation, and it is the single most consequential structural fact here.

It also explains a discrepancy anyone cross-checking this product will meet. The public deposited structure for this CAS gives C147H237N43O43S; the product states C147H238N44O42S. Those differ by one oxygen removed and one nitrogen and one hydrogen added, precisely the difference between a free acid and an amide. The deposited record describes the acid, the product the amide, and the stated weight settles which is meant: the amide computes to 3325.85, the acid to 3326.83.

The product's formula is therefore correct and should not be reconciled toward the public record. Three independent things agree: the substitution arithmetic, the stated weight, and the page's own description of the peptide as amidated. Treating the divergence as an error would introduce one.

The amidation matters practically as well as bibliographically. A free C-terminal carboxyl carries negative charge at neutral pH and an amide does not, so the molecule sits one unit more positive than the same sequence as a free acid. It also removes the handle carboxypeptidases act on.

The rest of the composition reinforces that. Of forty-four nitrogens, twenty-eight are backbone amides and one the C-terminal amide, leaving fifteen on side chains; of forty-two oxygens, twenty-eight belong to the backbone, leaving fourteen. Fifteen side-chain nitrogens against fourteen oxygens is nitrogen-rich, indicating abundant basic side chains and net positive charge at neutral pH.

There is one sulfur, and the deposited structure identifies it as a methionine thioether, with no disulfide and no free thiol. One sulfur could not form an internal bridge in any case, since that requires two.

Reconstitution and handling

Sterile water is the default solvent. Where a vial dissolves reluctantly, mildly acidic conditions are the right escalation for a basic peptide, since lowering pH increases net positive charge and solubility.

Add diluent slowly down the inside wall of the vial, swirl gently, and let the solution clarify. Do not vortex; it introduces foam without dissolving anything faster.

No reducing agent is needed: the single sulfur is a thioether, and there is no disulfide to protect.

Adsorption deserves attention on a basic peptide: a net positive molecule binds negatively charged surfaces, so borosilicate glass is a poorer choice than low-protein-binding 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.

Methionine oxidation is the named sulfur liability, adding sixteen units as the sulfoxide. Air, warmth and light accelerate it, the ordinary argument for a sealed, cold, dark vial.

The C-terminal amide is a second, less familiar liability. Hydrolysis converts the peptide to its free-acid form, adding about one unit and restoring the negative charge the amide removes. It is slow near neutral pH and accelerated at both extremes, so near-neutral storage is the control.

The high side-chain nitrogen count indicates asparagine or glutamine may sit among the basic residues, both deamidating to their acidic counterparts and also adding about one unit. Without a sequence this page will not name positions.

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

How VIP is tested

Reversed-phase HPLC establishes chromatographic purity as area percent. A basic, charged peptide of this size retains moderately on a standard C18 column, and trifluoroacetic acid in the mobile phase helps both retention and peak shape.

Area percent is a chromatographic measure and not peptide content by weight. Solid-phase synthesis delivers a salt, and on a basic peptide the counter-ion is a substantial proportional share of the vial contents.

Mass spectrometry confirms identity against 3325.85, and one comparison deserves care. A result near 3326.8 indicates not a heavier impurity but the free-acid form, whether from hydrolysis of the amide or synthesis of the wrong terminus. Deamidation of an asparagine or glutamine also adds about one unit, so a single mass reading cannot distinguish the two; chromatography separates them, since loss of the C-terminal amide shifts net charge and retention more than a side-chain deamidation does.

A result sixteen units high indicates methionine sulfoxide.

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

Handling FAQ

The formula here differs from the public database. Which is right? The product's. The public record describes the free-acid form; this material is amidated, which accounts for the difference exactly: one oxygen fewer, one nitrogen and one hydrogen more. The stated 3325.85 corresponds to the amide, not the acid at 3326.83.

Does the C-terminal amide need any particular handling? Only near-neutral pH. Amide hydrolysis converts the peptide to its free-acid form, a genuine change of substance rather than simple degradation, and both pH extremes accelerate it.

Full specifications for VIP.