What mass should an IGF-1 LR3 certificate show?

There is no PubChem entry for IGF-1 LR3, so there is no database mass to quote. The expected value has to be calculated from the 83-residue sequence, allowing for the three disulfide bonds. A good certificate states that expected mass, the observed deconvoluted mass and the sequence it assumed, so you can repeat the calculation yourself.

Can a test tell IGF-1 LR3 from ordinary IGF-1?

Yes. Human IGF-I is a 70-residue chain, while IGF-1 LR3 adds a 13-residue extension and has arginine at position 3, so it is substantially heavier. Intact mass by LC-MS separates them, and N-terminal sequencing confirms whether the chain starts Met-Phe-Pro-Ala-Met, the extension, or Gly-Pro, plain IGF-I.

Is IGF-1 LR3 a peptide or a protein for testing purposes?

Analytically it behaves like a small protein: 83 residues, three disulfides and production in bacteria. Protein-style checks therefore add information a short-peptide panel would not, such as disulfide mapping, size-based methods for dimers and other aggregates, and, where available, host cell protein assays. Agree which of these are included before the sample is sent.

One of the 30 compound testing profiles

IGF-1 LR3

IGF-1 LR3 is an 83-residue recombinant analogue of IGF-I with three disulfide bonds and no PubChem formula or mass, so a test has to state the mass it calculated from the sequence and show that the disulfides are in the native arrangement, because misfolded isomers have exactly the same mass.

IGF-1 LR3 is a recombinant analogue of insulin-like growth factor I in which Glu3 is replaced by arginine and a 13-residue N-terminal extension is attached, first described as Long [Arg3]-IGF-I (Francis et al., 1992; Milner et al., 1995).

Test your IGF-1 LR3

Identity card

Formula: Not a single molecule (see note)
Average mass: Not published
Monoisotopic mass: Not published
Length: 83 residues
Modifications: 13-residue N-terminal extension MFPAMPLSSLFVN; Arg in place of Glu at IGF-I position 3; Three disulfide bonds within the IGF-I domain
Also sold as: Long R3 IGF-1, LR3-IGF-I, Long [Arg3]-IGF-I, Long R3 IGF-I
Sequence: MFPAMPLSSLFVNGPRTLCGAELVDALQFVCGDRGFYFNKPTGYGSSSRRAPQTGIVDECCFRSCDLRRLEMYCAPLKPAKSA
Note: No PubChem record was found for IGF-1 LR3, and no source opened for this profile states its formula or mass, so those fields are left empty. The sequence is assembled from cited sources rather than copied from one: Francis et al. (1992) describe Long [Arg3]-IGF-I as [Met1]-pGH(1-11)-Val-Asn-[Arg3]-IGF-I; Milner et al. (1995) give that 13-residue extension as Met-Phe-Pro-Ala-Met-Pro-Leu-Ser-Ser-Leu-Phe-Val-Asn; the IGF-I part is the 70-residue mature human chain (UniProt P05019, residues 49 to 118) with Glu3 replaced by Arg. The three IGF-I disulfides are taken from UniProt P05019.

Source: Milner SJ et al. Mutations in the B-domain of insulin-like growth factor-I influence the oxidative folding to yield products with modified biological properties. Biochem J. 1995;308(Pt 3):865-71, 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. J Mol Endocrinol. 1992;8(3):213-23, Insulin-like growth factor 1 (P05019).

Compare the mass printed on a certificate with the values above. The mass checker explains charge states and which mass a lab usually reports.

What usually goes wrong with IGF-1 LR3. Documented failure modes, with sources.

Misfolded disulfide isomers with the same mass

The oxidative folding of IGF-I yields two major disulfide folding isomers, the native form and a main alternative (Milner et al., 1995). In the same study the N-terminal extension raised the yield of the native isomer, most of all for Long-[Arg3]IGF-I, but the alternative isomer was still present in reduced proportions. A misfolded isomer has the same atoms and mass as the native protein, so intact mass cannot tell them apart. ICH guidance lists mismatched disulfide-linked forms among the variants that chromatographic methods such as HPLC can detect, and recommends peptide mapping under reducing and non-reducing conditions to locate disulfide bridges (ICH Q6B).

Other IGF-I analogues under similar names

Francis and colleagues made three Long analogues: Long IGF-I (authentic IGF-I sequence), Long [Gly3]-IGF-I and Long [Arg3]-IGF-I, and compared them with the truncated des(1-3)IGF-I (Francis et al., 1992). [Arg3]-IGF-I and [Gly3]-IGF-I without the extension were also produced (King et al., 1992), and plain human IGF-I is a 70-residue chain (UniProt P05019). Each differs in length or in the residue at position 3, so intact mass shows which one a vial holds.

A chemically cleavable Asn-Gly junction

In the original expression system, the dipeptide Val-Asn was placed before the N-terminal Gly of IGF-I to give a hydroxylamine-sensitive Asn-Gly bond, which was cut to release IGF-I (King et al., 1992). The Long analogues keep that junction: the extension ends in Val-Asn and the IGF-I chain follows (Francis et al., 1992). Cleavage there would leave a 70-residue [Arg3]-IGF-I, much lighter on LC-MS or SDS-PAGE, and an N-terminal sequence starting Gly-Pro-Arg instead of Met-Phe-Pro-Ala-Met.

Three methionines and other protein variants

IGF-1 LR3 carries methionine at positions 1 and 5 of its extension and a third in the IGF-I chain. ICH guidance lists deamidated, isomerised, mismatched disulfide-linked and oxidised forms, truncated forms, and aggregates such as dimers as product-related variants to detect by HPLC, electrophoresis, mass spectrometry or size exclusion chromatography (ICH Q6B). For material made outside a regulated setting, methionine oxidation is the first of these to look for.

Which tests matter most

LC-MSMeasures intact mass to confirm the 83-residue LR3 analogue rather than IGF-I, Long IGF-I or the [Gly3] variant, and finds oxidised or truncated forms.
Peptide mappingMapping under reducing and non-reducing conditions locates the disulfide bridges, which intact mass cannot.
HPLC-UVHPLC established purity in the original IGF-I and [Arg3]-IGF-I production work and can detect mismatched disulfide forms.
Amino acid analysisQuantitative amino acid analysis can determine protein content, independent of salt and water.

Reading IGF-1 LR3 results

An IGF-1 LR3 certificate has to state its own expected mass and the sequence it used. In mass spectrometry, each disulfide shows as a mass 2 Da below the sum of its free-thiol parts (Lakbub et al., 2018), so with three disulfides the folded protein is 6 Da lighter than the fully reduced chain. A report that compares against the wrong form will appear to fail.

In the original production work, purity of IGF-I and its [Arg3] and [Gly3] analogues was established by HPLC together with N-terminal sequence analysis (King et al., 1992). For IGF-1 LR3, N-terminal sequencing is direct evidence that the 13-residue extension is present.

IGF-1 LR3 is made in bacteria, so ICH Q6B logic applies: host cell proteins and host cell DNA are process-related impurities, and host cell proteins need a sensitive assay such as an immunoassay (ICH Q6B). A standard identity, purity and amount panel does not measure them. Where they matter, ask the partner laboratory in advance whether such assays are available when testing opens.

Public Tested.ph results

No public IGF-1 LR3 records yet

Each public IGF-1 LR3 record will appear here with its identity, HPLC purity and measured amount against the label, once the first vial is tested.

FIG 13Amount against the label

Questions about testing IGF-1 LR3

What mass should an IGF-1 LR3 certificate show?: There is no PubChem entry for IGF-1 LR3, so there is no database mass to quote. The expected value has to be calculated from the 83-residue sequence, allowing for the three disulfide bonds. A good certificate states that expected mass, the observed deconvoluted mass and the sequence it assumed, so you can repeat the calculation yourself.
Can a test tell IGF-1 LR3 from ordinary IGF-1?: Yes. Human IGF-I is a 70-residue chain, while IGF-1 LR3 adds a 13-residue extension and has arginine at position 3, so it is substantially heavier. Intact mass by LC-MS separates them, and N-terminal sequencing confirms whether the chain starts Met-Phe-Pro-Ala-Met, the extension, or Gly-Pro, plain IGF-I.
Is IGF-1 LR3 a peptide or a protein for testing purposes?: Analytically it behaves like a small protein: 83 residues, three disulfides and production in bacteria. Protein-style checks therefore add information a short-peptide panel would not, such as disulfide mapping, size-based methods for dimers and other aggregates, and, where available, host cell protein assays. Agree which of these are included before the sample is sent.

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. J Mol Endocrinol. 1992;8(3):213-23, Journal of Molecular Endocrinology (PubMed)
Milner SJ et al. Mutations in the B-domain of insulin-like growth factor-I influence the oxidative folding to yield products with modified biological properties. Biochem J. 1995;308(Pt 3):865-71, Biochemical Journal (PMC)
King R et al. Production and characterization of recombinant insulin-like growth factor-I (IGF-I) and potent analogues of IGF-I, with Gly or Arg substituted for Glu3, following their expression in Escherichia coli as fusion proteins. J Mol Endocrinol. 1992;8(1):29-41, Journal of Molecular Endocrinology (PubMed)
Insulin-like growth factor 1 (P05019), UniProt
ICH Q6B: Specifications, test procedures and acceptance criteria for biotechnological/biological products, International Council for Harmonisation
Lakbub JC et al. Recent mass spectrometry-based techniques and considerations for disulfide bond characterization in proteins. Anal Bioanal Chem. 2018;410(10):2467-2484, Analytical and Bioanalytical Chemistry (PMC)

Last reviewed 6 Oct 2026.