Quick answer
IGF-1 LR3 is an 83-residue, three-disulfide recombinant protein (about 9.1 kDa), so a lot needs purity, identity and a folding check, not just one HPLC percentage.
- Purity: RP-HPLC (plus SEC for aggregates) from the chromatogram, not a bare percentage
- Identity: intact-mass MS against the theoretical mass of the LR3 sequence
- Folding: same mass does not mean same structure; use non-reduced mapping or a bioassay
- Paperwork: lot-matched COA; see the COA page and product page
- Research use: For laboratory research use only; not for human consumption.
For laboratory research use only; not for human consumption.
IGF-1 LR3 is a larger, disulfide-bonded recombinant protein rather than a short synthetic peptide, so verifying a lot involves one more question than sequence and purity: did the molecule fold correctly? This guide explains which analytical methods answer which question, what each one cannot tell you, and what a useful certificate of analysis (COA) for this compound should contain. Background on the molecule itself is in the IGF-1 LR3 research overview.
Why IGF-1 LR3 is harder to verify than a short peptide
Most catalog peptides are 5 to 40 residues, made by solid-phase synthesis, and have either no disulfide bonds or one. IGF-1 LR3 is different on three counts:
- Size. It is an 83-residue analog of the 70-residue native IGF-1, with a mass of roughly 9.1 kDa (native IGF-1 is about 7.65 kDa). The listed formula on the IGF-1 LR3 product page is C400H625N111O115S9.
- Two sequence changes. The "R3" is a glutamate-to-arginine substitution at position 3, and the "Long" is an N-terminal extension of 13 residues. Both changes reduce binding to IGF-binding proteins in assay systems.
- Three intramolecular disulfide bonds. Native IGF-1 has six cysteines paired into three disulfides. Correct pairing is required for the receptor-binding conformation, and incorrect pairing produces isomers with the same atomic composition.
Because the molecule is typically produced by recombinant expression and refolded, rather than assembled residue by residue, the impurity profile also differs: misfolded isoforms, aggregates, truncations, host-cell proteins and endotoxin become relevant alongside the usual synthesis by-products.
The analytical toolkit and what each method answers
| Method | Question it answers | What it cannot tell you |
|---|---|---|
| Reversed-phase HPLC (RP-HPLC) | What fraction of detected UV signal is the main species; are there resolvable related species? | Identity; and co-eluting variants can hide under one peak |
| Size-exclusion HPLC (SEC) | Are dimers, oligomers or aggregates present? | Folding of the monomer |
| SDS-PAGE | Approximate molecular weight; gross fragments or aggregates | Precise mass; low-level impurities |
| Intact-mass spectrometry (ESI-MS) | Does the measured mass match the expected mass of the LR3 sequence? | Disulfide pairing: correct and scrambled forms have identical mass |
| Peptide mapping (digest + LC-MS) | Sequence coverage; with non-reduced vs. reduced maps, which cysteines are linked | Biological activity |
| Cell-based or binding assay | Does the material engage the IGF-1 receptor as expected? | Chemical identity on its own |
No single row is sufficient. A defensible lot record combines at least a chromatographic purity value and an identity measurement, and for this compound benefits from an orthogonal check of folding or function.
Reversed-phase HPLC and the purity figure
RP-HPLC separates species by hydrophobicity on a C4, C8 or C18 column with an acetonitrile gradient and typically detects at 214 or 220 nm (peptide bond) or 280 nm (aromatic residues). The reported purity is the area of the main peak divided by the total integrated area. The product page lists purity as ≥98% by HPLC; how to interpret such a figure, including integration thresholds and gradient choice, is covered in understanding HPLC purity.
For a protein of this size, several caveats apply. Misfolded isoforms often elute slightly earlier or later than the native fold, but a shallow gradient is needed to resolve them. A steep, short gradient can compress them into one apparently clean peak. Ask for the chromatogram itself, not only the percentage, and check the gradient time, column and detection wavelength.
SDS-PAGE and aggregation checks
SDS-PAGE is inexpensive and gives a quick view of apparent molecular weight. Run under non-reducing conditions, IGF-1 LR3 typically migrates faster than its reduced form because the intact disulfides keep the chain compact; running a reduced and non-reduced lane side by side is therefore a simple, informative check that disulfides are present. Gel methods are semi-quantitative and cannot see species close in size, so they complement rather than replace HPLC and mass spectrometry. Size-exclusion chromatography is the better quantitative tool for dimers and higher-order aggregates, which matter because aggregates can alter apparent concentration and assay behavior.
Mass spectrometry for identity
Electrospray mass spectrometry of the intact protein produces a charge-state envelope that is deconvoluted into a single neutral mass. That value should agree with the theoretical mass of the LR3 sequence, computed with all six cysteines in the oxidized, disulfide-bonded state, within the instrument tolerance (typically well under 1 Da for high-resolution instruments, a few Da for low-resolution ones). The distinction between oxidized and reduced states is itself useful: complete reduction of three disulfides adds about 6 Da, so a mass that fits the reduced form points to unfolded or incompletely oxidized material. The same logic exposes oxidized methionine (+16 Da per oxidation) and deamidation (+1 Da), both of which can appear in aged material. For a general comparison of the two techniques, see HPLC vs. mass spectrometry.
Why correct folding matters more here
A misfolded protein can carry exactly the same mass as the correctly folded form and may also co-elute or elute very close to it. Mass spectrometry alone cannot separate scrambled disulfide isomers, and a high HPLC percentage can still include them. What the researcher cares about, receptor engagement in a cell-signaling assay, depends on the three-dimensional structure set by the disulfides. That is why analytical confirmation of mass should be read alongside at least one of the following:
- non-reduced vs. reduced peptide mapping showing the expected cysteine linkages;
- a receptor-binding or cell-proliferation bioassay with a reference standard;
- a retention-time match to a characterized reference lot on a shallow-gradient method.
If a supplier can provide none of these, the lot is verified for mass and apparent purity, not for folding; record it that way in your own notes. Comparison with other IGF-1 forms, whose masses differ and are therefore distinguishable by MS, is in IGF-1 LR3 vs. IGF-1 DES.
Other impurities specific to recombinant proteins
- Endotoxin. Relevant for cell-culture work, since endotoxin can activate cells independently of the protein under study. It is measured by the LAL assay and reported in EU/mg.
- Host-cell proteins and nucleic acids. Low-level contaminants from the expression system; usually assessed by ELISA or gel, and rarely reported on routine research COAs.
- Counter-ions, moisture and excipients. Lyophilized protein often contains buffer salts; the vial label mass and net protein content are not necessarily the same number. Ask whether quantity was determined by UV absorbance, amino-acid analysis or weight.
- Chemical variants. Methionine oxidation, deamidation and N-terminal truncations, visible by MS and HPLC.
What a useful COA for IGF-1 LR3 contains
| COA element | What to look for |
|---|---|
| Lot number and test date | Matches the label on the vial received |
| HPLC purity | Percentage plus the chromatogram, column and gradient |
| Observed vs. theoretical mass | Both numbers stated, with the ion state or deconvolution method |
| Quantity per vial | Stated amount (the product page lists a 1 mg size) and how it was determined |
| Folding or activity data | Binding or bioassay result, or an explicit statement that it was not performed |
| Form and storage | Lyophilized powder; refrigerated, frozen for long-term storage, protected from heat, moisture and light |
The field-by-field reading guide is how to read a COA, and the general rationale for independent verification is in third-party testing explained. V8 publishes batch documentation on the COA page; the IGF-1 LR3 product page currently shows its COA status as in progress, so check that page for the current state of any lot you intend to order.
Verifying a received vial in your own lab
Independent checks are worthwhile for a compound where folding is the main risk. Before using a lot for a study, many labs run a quick non-reducing and reducing SDS-PAGE, a single RP-HPLC run against a retained reference, and a small bioassay with a dose-response curve. Record the lot number against every dataset. When reconstituting, express the stock as mg/mL (mass in the vial divided by diluent volume) using the reconstitution calculator, and avoid vigorous agitation, which can promote aggregation of proteins. Storage principles are in storing research peptides. For sourcing criteria rather than testing, see where to buy IGF-1 LR3, and for the compound itself see the IGF-1 LR3 research vial.
Frequently asked questions
Is a 98% HPLC purity enough to confirm IGF-1 LR3 is correctly folded?
No. HPLC measures how much of the detected signal is one peak. A misfolded isomer with the same mass can co-elute or sit close to the native form, so purity must be read together with mass and, ideally, a folding or activity check.
What mass should IGF-1 LR3 show on mass spectrometry?
About 9.1 kDa for the 83-residue sequence with all three disulfides intact. A value about 6 Da higher suggests reduced, unfolded material. Always compare to the theoretical mass stated on the COA.
Why is SDS-PAGE used for IGF-1 LR3 when HPLC exists?
It is a fast orthogonal check of apparent size and gross aggregation, and comparing reduced and non-reduced lanes shows whether disulfides are present. It is semi-quantitative, so it supplements HPLC.
Can mass spectrometry detect disulfide scrambling?
Not from intact mass alone, because scrambled and correct forms have identical mass. Non-reduced peptide mapping or a functional assay is needed.
Does IGF-1 LR3 need an endotoxin result?
For cell-culture work it is useful, because endotoxin can activate cells on its own. It is measured by the LAL assay and is not always reported on routine research COAs, so ask.
What does a batch-specific COA add over a product specification?
It ties purity and mass data to the exact lot on your vial. A product specification only states a target. Check the lot number on the COA against the vial label.
What does V8 state about IGF-1 LR3 purity?
The product page lists ≥98% HPLC purity, a 1 mg size and the formula C400H625N111O115S9, and says sequence and identity are reported on the certificate of analysis where published.
How should I express a reconstituted stock concentration?
As mg/mL: vial mass divided by diluent volume. For example, 1 mg in 1 mL is 1 mg/mL. The calculator returns the same figure.
Research Use Only. For laboratory research use only; not for human consumption. Supplied strictly for laboratory research and development, not for human or veterinary use, and not for any diagnostic or clinical purpose. This article is research education, not usage guidance.