IGF-1 LR3 (Long R3 IGF-1): preparation and storage
Intended for research use only. Not a medicinal product.
Contents (9 sections)
What Long and R3 mean
Francis and colleagues describe Long [Arg3]-IGF-I as an analogue with an N-terminal extension and substitution of Arg for Glu3 in the original IGF-I sequence. Repligen specifies a 13-residue extension for LONG R3. Check these features against the specification rather than treating the vial name as complete structural confirmation. [1,2]
Do not use native IGF-I or des(1-3)IGF-I molecular weight. Molarity needs the exact sequence and form of your product. If a method uses ng/mL, retain those units; an unnecessary molar conversion with the wrong mass adds an avoidable error.
IGF-binding proteins change the comparison
Francis compared the analogues across different cell systems. IGF-binding-protein interactions affected relative activity; cells without detectable IGFBP secretion gave another relationship to native IGF-I. Consequently, “LR3 is always more potent” is incomplete without a model description. [1]
Record serum, protein additives and cells. Low-serum results do not automatically transfer to another matrix. A lower signal does not prove chemical deterioration; first match the medium, timing and endpoint.
Dry product versus ready liquid
Repligen supplies LONG R3 as freeze-dried material and ready liquid. A catalogue does not determine your batch form; the label and COA do. Do not add a reconstitution volume to ready liquid or assume its concentration from another product. [2]
GroPep publishes a 10 mM HCl protocol for its dry material. This is that manufacturer procedure, not a universal Longeva recipe. Retain your own vehicle and reconstitution specification. Neutral or bacteriostatic water is not equivalent to an acid protocol simply because the volumes match. [3]
Adsorption, carrier and filtration
GroPep warns of IGF-peptide losses to plastic and glass during dilution and describes carrier protein for its working preparations. Existing proteins in low-serum media also affect the choice. Check recovery when transferring very dilute IGF-LR3 into new vessels. [3]
The same document warns about adsorption during filtration of dilute solutions and recommends low-protein-binding membranes. If filtration is required, measure recovery after it. Do not assume pre-filter and post-filter concentrations match or quietly add BSA to a carrier-free assay.
Calculations and actual content
Use quantitative content information when available. GroPep explains that dry mass includes residual moisture and counterions; weighing lyophilizate does not directly measure IGF mass. Do not convert all dry material into molarity without appropriate composition data. [3]
For an educational example, 1 mg/mL to 1 µg/mL is a 1:1000 dilution. It can be calculated as 1:100 followed by 1:10, recording volume and vehicle at each step. This is arithmetic, not an IGF-LR3 concentration recommendation. The vehicle control should reproduce both steps without the test factor.
Which measurements to compare
Receptor activation, cell growth and quantitative immunoassays are different tests. Repligen describes a LONG R3-specific ELISA with limited native IGF-I reactivity: antibody selection changes what is measured. Verify that an IGF-I kit is suitable for LR3 rather than assuming it is. [2]
Compare batches using a defined reference and the same cells. Analyse fresh and stored samples together when investigating storage. Resolve IGFBP, vehicle and filtration differences before concluding that degradation occurred.
Storage: the specification overrides a general rule
Some dry peptides use freezer storage for the long term and refrigeration for short use, but IGF products show why this is not universal. GroPep explicitly specifies 2–8 °C for its lyophilizate and a separate frozen regime for its acidic solution. Repligen has its own dry and liquid formulations. [2,3]
Do not assign freezer storage to every IGF-LR3 product based on its name. Your LOT needs form-specific conditions and duration. A refrigerated week or month must be supported. When freezing is permitted, use working aliquots and thaw records; dry-material shelf life does not transfer to solutions.
Frequently asked questions
Is this native IGF-I?
No. LR3 has defined structural changes and different IGFBP interactions relevant to comparisons.
Can a dilute solution be filtered without checking recovery?
Do not assume full recovery: membrane adsorption is a documented risk, especially for dilute preparations.
Why is there no single opening-based period?
Dry material, ready liquid and reconstituted solution have different formulations and conditions; use the documentation for the actual form.
Sources
- Francis GL et al. Novel recombinant fusion protein analogues of insulin-like growth factor (IGF)-I indicate the relative importance of IGF-binding protein and receptor binding for enhanced biological potency. Journal of Molecular Endocrinology, 1992. DOI (Digital Object Identifier, a permanent link to a scientific paper) verified; primary abstract read.
- Repligen: LONG R3 IGF-I. Analogue, supplied forms and specific ELISA information read 26 October 2026.
- GroPep Bioreagents: Handling IGF-I, IGF-II and IGF Analogues, WDHN-01.05. Full protocol read 26 October 2026; manufacturer-specific conditions, not another batch recipe.
Product and current sizes · Monograph and research · COA
A laboratory guide for research material; no human-use regimen is provided.
End of article
IGF-1 LR3
for laboratory research
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