IGF-1 LR3

What IGF-1 LR3 is, structurally

IGF-1 LR3 is the parent IGF-1 sequence carrying a thirteen-residue N-terminal extension and one substitution at position three, giving eighty-three residues where the parent has seventy. The name encodes both changes: "Long" for the extension, "R3" for the arginine that replaces the parent's glutamate.

Both parts of that description are checkable against the supplied specification, and both hold. Adding the extension and the single substitution to the parent's published mass predicts 9111.51 against the stated 9111.45, a difference well inside rounding. The sulfur count agrees independently: nine sulfurs, being six cysteines paired into three disulfide bonds, the parent's one methionine, and two more methionines carried in the extension.

The three disulfides are the dominant handling fact, exactly as in the shorter family members. Reducing agents must be kept away from this material entirely. Dithiothreitol, TCEP and 2-mercaptoethanol break the cross-links, and reduced material is a different substance from what the vial contains.

Disulfide exchange is the subtler risk. It is catalysed by thiolate, which forms as pH rises, so alkaline conditions let the three bonds reshuffle into wrong pairings. Scrambled material is isomeric with correct material, sharing its formula and its mass, so this is a failure ordinary mass spectrometry cannot see.

Where this molecule differs from the shorter forms is the methionine count. Three thioethers means three independent oxidation sites rather than one, so the accessible oxidised states run to sixteen, thirty-two and forty-eight units above the expected mass. Two of those three sit in the N-terminal extension, which is also markedly hydrophobic, and that extension should be expected to increase retention on a reversed-phase column relative to the parent.

Reconstitution and handling

Sterile water is the default solvent. Where a buffer is needed, keep it at or below neutral pH, since mildly acidic to neutral conditions suppress thiolate-mediated disulfide exchange while alkaline conditions promote it.

Add diluent down the inside wall of the vial, swirl gently, and let the solution clarify. Vortexing introduces foam without dissolving anything faster, and mechanical stress is better avoided on a folded, cross-linked molecule of this size.

Do not add a reducing agent, for the reason above.

Adsorptive loss deserves allowance at low concentration, with low-protein-binding tubes reducing it. At just over nine kilodaltons this is the largest of the three related products, and surface losses scale accordingly.

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. Freeze-thaw is a greater liability for a folded, cross-linked molecule than for a short linear peptide, because the damage is structural rather than only chemical.

Oxidation deserves more attention here than on the shorter forms. With three methionines the molecule presents three targets rather than one, and the first sixteen-unit addition is correspondingly more likely per unit time. Air exposure, warmth and light all accelerate it, so a sealed, cold, dark vial is doing real work.

Disulfide scrambling remains the other route, and remains the one no mass measurement will report.

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

How IGF-1 LR3 is tested

Reversed-phase HPLC establishes chromatographic purity as area percent, and the hydrophobic extension gives this molecule better retention than the parent, which makes the separation from truncated or deletion sequences more tractable than it would otherwise be.

The most informative check is comparative. Running the material alongside a deliberately reduced aliquot separates correctly folded material from reduced or scrambled forms, which differ in retention even where they do not differ in mass.

Area percent is a chromatographic measure and not peptide content by weight. Solid-phase synthesis delivers a salt, and residual trifluoroacetate is its own impurity class.

Mass spectrometry confirms identity against 9111.45. A result six units high indicates fully reduced material, since each disulfide formed removes two hydrogens. Results sixteen, thirty-two or forty-eight units high indicate one, two or three oxidised methionines. A result near 7649 or 7365 is not this compound at all, but the parent or the des(1-3) form, both of which are sold separately.

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

Handling FAQ

Can a reducing agent be used on this material? No. It holds three disulfide bonds, and dithiothreitol, TCEP or 2-mercaptoethanol will break them. Reduced material is a different substance from what the vial contains, and removing the reagent afterwards does not restore the original pairings.

Why does this oxidise more readily than the shorter IGF-1 forms? Because it carries three methionines rather than one, two of them in the N-terminal extension. Each is an independent site, so the molecule presents three chances for the same sixteen-unit addition.

Full specifications for IGF-1 LR3.