IGF-1 LR3 Molecular Weight, Sequence & CAS Reference

Introduction: Structural Overview of Long R3 IGF-1

Long R3 Insulin-like Growth Factor-1 (IGF-1 LR3) is a synthetic recombinant analog of human insulin-like growth factor-1 engineered specifically to modify binding affinity to endogenous IGF-binding proteins (IGFBPs). In biochemical literature, the peptide is frequently evaluated in cell culture, tissue engineering, and receptor-ligand kinetics studies. Understanding the precise molecular specifications of IGF-1 LR3 is essential for quantitative analytical chemistry, molar concentration calculations, and high-throughput cellular assays.

While naturally occurring human IGF-1 consists of a 70-amino-acid single-chain polypeptide, IGF-1 LR3 contains an 83-amino-acid sequence resulting from two distinct structural modifications: the substitution of Glutamic acid (Glu) with Arginine (Arg) at position 3, and an additional 13-amino-acid N-terminal extension peptide. These modifications significantly alter the physical, chemical, and pharmacokinetic profile of the peptide in experimental models, making precise mass and sequence verification a critical prerequisite for laboratory investigation.

Primary Amino Acid Sequence and Structural Architecture

The primary structure of IGF-1 LR3 consists of 83 amino acid residues linked by standard peptide bonds, featuring three intramolecular disulfide bridges that maintain its tertiary globular conformation. The complete single-letter amino acid sequence for the free base variant is published as follows:

Met-Phe-Pro-Ala-Met-Pro-Leu-Ser-Ser-Leu-Phe-Val-Asn-Gly-Pro-Arg-Thr-Leu-Cys-Gly-Ala-Glu-Leu-Val-Asp-Ala-Leu-Gln-Phe-Val-Cys-Gly-Asp-Arg-Gly-Phe-Tyr-Phe-Asn-Lys-Pro-Thr-Gly-Tyr-Gly-Ser-Ser-Ser-Arg-Arg-Ala-Pro-Gln-Thr-Gly-Ile-Val-Asp-Glu-Cys-Cys-Phe-Arg-Ser-Cys-Asp-Leu-Arg-Arg-Leu-Glu-Met-Tyr-Cys-Ala-Pro-Leu-Lys-Pro-Ala-Lys-Ser-Ala

Single-letter notation: MFPAMPLSSLFVNGPRTLCGAELVDALQFVCGDRGFYFNKPTGYGSSSRRAPQTGIVDECCFRSCDLRRLEMYCAPLKPAKSA

The sequence modifications are twofold: first, the 13-amino-acid N-terminal leader peptide sequence (MFPAMPLSSLFVN) is derived from bovine growth factor expression constructs; second, the native Glutamic acid at position 3 of the native IGF-1 domain is replaced by Arginine (denoted as R3). This structural alteration introduces a significant steric and electrostatic disruption in the domain responsible for binding IGF-binding proteins (IGFBPs), while preserving the contact residues necessary for activation of the type 1 IGF receptor (IGF-1R).

Molecular Formula, Molecular Weight, and Mass Spectrometry Verification

The theoretical molecular weight of IGF-1 LR3 is calculated based on the elemental composition of its 83 amino acid residues alongside its three intramolecular disulfide crosslinks (forming six Cysteine residues participant in Cys-Cys bonds).

The empirical molecular formula of native free-base IGF-1 LR3 is C400H625N111O121S9, yielding a calculated monoisotopic mass of approximately 9,111.5 Dalton (Da) and an average molecular weight of approximately 9,111.6 Da (or 9.11 kDa). Due to variations in micro-heterogeneity, oxidation states, and isotopic distributions, exact mass verification using Matrix-Assisted Laser Desorption/Ionization Time-of-Flight (MALDI-TOF) or Electrospray Ionization Liquid Chromatography-Mass Spectrometry (ESI-LC-MS) is standard protocol for quality assurance.

When reviewing analytical data on a certificate of analysis, researchers should distinguish between the theoretical mass of the monoisotopic peptide and the observed mass-to-charge (m/z) ratios generated during ionization. Because IGF-1 LR3 is a large polypeptide, multi-charged ion species (such as [M+7H]7+, [M+8H]8+, and [M+9H]9+) are routinely observed in positive ESI-MS spectra. Confirmatory testing requires deconvoluting these multi-charged peaks back to the parent molecular mass of 9,111.6 ± 2.0 Da.

CAS Registry Numbers and Chemical Database Identifiers

Chemical abstracts service (CAS) identification numbers provide unambiguous indexing across international scientific literature and chemical inventory databases. However, because recombinant peptides and custom synthetic analogs undergo distinct registration paths depending on production methodology and salt form, multiple reference numbers exist within commercial and academic registries.

The primary recognized CAS Registry Number for Long R3 IGF-1 base sequence is 946870-92-4. In some legacy biological databases and catalog registries, reference numbers such as 143045-27-6 or broader generic entries for human insulin-like growth factor-1 analogs are cited. Researchers compiling chemical safety data sheets (SDS) or regulatory inventory documentation should utilize CAS 946870-92-4 when cataloging the specific 83-amino-acid recombinant sequence.

In addition to CAS indexing, the compound is identified in public chemical repositories under PubChem CID 16132435 or as a recombinant protein entity in UniProt under modified human IGF1 sequence constructs. When cross-referencing suppliers across all research peptides, verifying both the structural sequence and CAS designation ensures structural identity prior to ordering.

Peptide Counterion Salt Forms: TFA vs. Acetate & Net Peptide Content

Synthetic and recombinant peptides are isolated via reverse-phase high-performance liquid chromatography (RP-HPLC) utilizing mobile phase modifiers. Consequently, the final lyophilized powder exists as a peptide salt rather than a pure free base. The choice of counterion—typically Trifluoroacetate (TFA) or Acetate—has direct implications for net peptide content and molar calculations in physical biochemistry.

In standard RP-HPLC purification using trifluoroacetic acid as an ion-pairing agent, basic side chains (such as Lysine, Arginine, and the N-terminal amine) form non-covalent salts with TFA ions (CF3COO-). Because IGF-1 LR3 contains multiple basic residues (including 7 Arginine, 3 Lysine, and 1 N-terminal amine), a substantial mass fraction of the lyophilized lyophilizate consists of bound counterions and residual hydration water. Typically, the net peptide content (purity by weight) of a TFA salt ranges between 70% and 85%, with the remainder comprising counterions and bound moisture.

For quantitative in vitro studies where exact molarity is mandatory, researchers must adjust mass measurements based on the Net Peptide Content (NPC) reported on the batch-specific Certificate of Analysis (COA). To convert total gross mass to net active peptide mass, apply the following formula:

Net Peptide Mass (mg) = Gross Lyophilized Mass (mg) × [Net Peptide Content (%) / 100]

Failure to account for counterion mass lead to significant discrepancies in dose-response curves and receptor binding kinetics. For researchers requiring alternative salt formulations or detailed batch adjustments, PX1 Research provides lot-specific mass spec and counterion analysis across its full catalog.

Preclinical Pharmacodynamics and Receptor Affinity

In vitro models demonstrate that native IGF-1 binds to high-affinity soluble IGF-binding proteins (IGFBPs 1 through 6), which regulate its biological activity and clearance rate by sequestering free ligand away from the cell-surface Type 1 IGF Receptor (IGF-1R). Preclinical studies suggest that the substitution of Glutamic acid with Arginine at position 3 reduces the binding affinity of IGF-1 LR3 for IGFBPs by more than 1,000-fold compared to native IGF-1.

Simultaneously, the 13-amino-acid N-terminal extension introduces conformational flexibility that further impairs IGFBP complex formation without abolishing the ligand's ability to activate the tyrosine kinase domain of IGF-1R. In vitro cell culture models—including myoblast cell lines, chondrocytes, and primary hepatocyte cultures—indicate that this reduced binding to inhibitory proteins results in an elevated concentration of unbound, biologically active peptide in culture media.

Consequently, preclinical assays assessing cell proliferation, protein synthesis signaling (via the Akt/mTOR cascade), and glucose uptake frequently report prolonged biological activity for IGF-1 LR3 relative to wild-type IGF-1. However, all mechanisms described in published literature represent preclinical or in vitro observational data and must not be extrapolated to clinical or therapeutic contexts.

Comparative Analysis: Structural Differences Across the IGF Family

To select the appropriate research tool, investigators frequently compare IGF-1 LR3 against related growth factors and truncated analogs within the growth factor superfamily. The table of comparative features highlights distinct differences in sequence length, molecular weight, and target interactions.

Comparing structural properties across related peptides in the class highlights important functional distinctions. While IGF-1 LR3 retains an 83-residue modified structure designed to bypass IGFBPs, IGF-1 DES is a truncated 67-amino-acid variant lacking the first three N-terminal residues (Gly-Pro-Glu), which similarly reduces IGFBP binding but displays altered receptor internalisation kinetics. By contrast, MGF (Mechano Growth Factor) represents a splice variant of the IGF-1 gene containing a unique C-terminal E-domain sequence that targets distinct local tissue repair pathways independently of systemic IGF-1R saturation. Researchers evaluating systemic versus localized signaling pathways can review detailed specifications for these analogs across our research database or explore bulk account options for institutional projects via our wholesale portal.

Solubility, Reconstitution, and Solution Stability

Lyophilized IGF-1 LR3 is a hydrophobic-hydrophilic balanced polypeptide that exhibits specific solubility parameters depending on solvent pH and ionic strength. For optimal reconstitution in laboratory environments, adherence to validated reconstitution protocols is required to prevent aggregation or precipitation.

Reconstitution in neutral, unbuffered water or high-salt physiological saline can lead to aggregation or incomplete dissolution due to the peptide's iso-electric point and tertiary folding characteristics. Standard laboratory protocol recommends initial reconstitution in sterile 10 mM to 100 mM acetic acid or 0.1 M hydrochloric acid (pH 2.0 to 3.0) to achieve complete solubilization. Once fully dissolved, the solution can be diluted into working buffers such as Phosphate-Buffered Saline (PBS) containing 0.1% Bovine Serum Albumin (BSA) or Human Serum Albumin (HSA) as a carrier protein to minimize non-specific adsorption to glass or plastic container walls.

To calculate precise volumetric dilutions for micro-molar cell culture assays, laboratory personnel should utilize the PX1 Research reconstitution calculator. Reconstituted stock solutions stored at 2–8°C are stable for short-term evaluation, while long-term storage requires master aliquoting and storage at -80°C to avoid repeated freeze-thaw cycles.

Analytical Quality Metrics: HPLC, Mass Spec, and Endotoxin Standards

Because small impurities, truncated fragments, or bacterial endotoxins can confound delicate cell culture experiments and receptor binding assays, rigorous analytical testing is imperative. PX1 Research enforces strict quality assurance protocols on every lot of research-grade peptides manufactured in USA-based, GMP-compliant facilities.

Purity is quantified using reverse-phase HPLC paired with UV detection at 214 nm and 280 nm, ensuring single-peak homogeneity greater than or equal to 98.0%. Mass identity is confirmed by high-resolution ESI-MS, verifying that the observed molecular mass matches the theoretical calculated weight of 9,111.6 Da within strict analytical tolerances.

Furthermore, because cell culture media and enzymatic assays are sensitive to lipopolysaccharide contamination, all lots undergo Chromogenic Reagent Kinetic LAL (Limulus Amebocyte Lysate) testing to verify endotoxin levels are maintained below stringent limits (<0.05 EU/mg). Testing is validated by independent ISO 17025 accredited analytical laboratories, with downloadable lot-specific COAs available directly on our platform.

Technical Summary Sheet for Procurement & Documentation

Below is a consolidated summary of physical, chemical, and analytical parameters for Long R3 IGF-1 to assist procurement officers and principal investigators in completing chemical inventory records:

Compound Name: Long R3 Insulin-like Growth Factor-1 (IGF-1 LR3) Sequence Length: 83 Amino Acids Calculated Molecular Weight: ~9,111.6 Da Empirical Formula: C400 H625 N111 O121 S9 CAS Registry Number: 946870-92-4 Physical Form: Lyophilized white powder Counterion Form: Trifluoroacetate (TFA) or Acetate Purity Standard: ≥ 98.0% by RP-HPLC Source Material: USA-manufactured, ISO 17025 accredited COA verification Primary Application: Laboratory in vitro and preclinical research use only