IGF-1 LR3 lab tests

IGF-1 LR3 is a recombinant fusion protein, not a synthetic peptide. Its parent, native human IGF-1, is a 70-residue single chain with three intramolecular disulfide bridges and a molecular weight of 7,649 Da — FDA's figure, from the approved mecasermin label (mature parent sequence: UniProt P05019). LR3 adds an N-terminal extension and a substitution at position 3, where native mature IGF-1 carries glutamate. The specification vendors quote for the finished analogue — 83 amino acids, an extension written as MFPAMPLSSLFVN, and a molecular weight of roughly 9,111 Da — has no source Peptigrity could find: a full-text Europe PMC search for that extension sequence returns zero hits across the indexed biomedical literature.

The founding paper (Francis, Ross, Ballard et al., Journal of Molecular Endocrinology, 1992, PMID 1378742) describes analogues comprising "an IGF-I sequence and the first 11 amino acids of methionyl porcine growth hormone" — eleven residues, not thirteen, which gives 81 residues rather than 83. The market figure is not shown to be wrong; it is unsourceable, and the primary paper appears to disagree with it. A wrong number can be corrected, while an unsourceable number cannot be checked at all: a certificate reporting a mass has nothing authoritative to be checked against, because the usual comparator is the same unsourced 9,111 Da circulating on the vendor pages being audited.

Mass spectrometry can still exclude the most plausible substitution. Native IGF-1 at 7,649 Da is far enough from any plausible LR3 mass to be unambiguous, so a batch-matched spectrum should at minimum exclude it — but a result reading "approximately 9,000 Da" is a measurement, not an identity confirmation. A second failure sits behind the first: the three disulfide bridges must pair correctly, incorrectly folded IGF-1 has exactly the same mass as correctly folded IGF-1 and is biologically inactive, and no routine certificate of analysis reports folding at all. HPLC cannot help, because a homogeneous sample of misfolded protein returns a clean chromatogram.

• Ask where the 9,111 Da figure comes from. A vendor who can produce a primary source has provided something new; a vendor who repeats the number without one has copied a specification rather than characterised a product. This check runs on the paperwork, not the vial.
• A batch-matched mass spectrum that at minimum excludes native IGF-1 at 7,649 Da, tied to the lot in hand rather than a specimen certificate from an earlier batch.
• Disulfide pairing: no routine certificate reports it, and mass spectrometry cannot see pairing at all. A vendor claiming MS proves correct folding is claiming something it cannot show.
• The word "recombinant" and a named expression system on the product page. Francis and colleagues expressed LR3 in E. coli in 1992, and a 2023 paper describes expression in Pichia pastoris. An 80-odd-residue disulfide-bonded protein sits at or beyond the edge of solid-phase peptide synthesis, so a page describing LR3 as a synthetic peptide made by SPPS is describing a route that does not produce this molecule.
• Fill quantity as its own line: quantity variance on this compound ran +1% to +72% (verified August 2026), and one June 2026 sample tested 72% over label — direct evidence that fill quantity is uncontrolled. It sits alongside the identity checks because hypoglycaemia is the signature adverse effect of the approved parent drug, at 42% incidence in a monitored paediatric population.
• Endotoxin (LAL) results are rarely reported on this compound.