What IGF-1 LR3 is
IGF-1 LR3, or Long R3 IGF-1 (also written IGF1 LR3, IGF1-LR3 and IGF 1 LR3), is a recombinant analogue of human insulin-like growth factor 1. Native IGF-1 is a 70-residue single-chain protein with three disulphide bonds. The LR3 variant carries two modifications: a substitution of arginine for the glutamate at position 3, and a 13-residue extension at the N-terminus derived from a porcine growth hormone sequence, giving 83 residues in all. It was developed at GroPep in Adelaide in the late 1980s and early 1990s, and the arginine substitution in particular sharply reduces its affinity for the six IGF-binding proteins that otherwise sequester IGF-1 in serum and in culture media.
Because it escapes the binding proteins while retaining activity at the IGF-1 receptor, LR3 IGF-1 became a standard growth factor supplement in serum-free media for mammalian cell lines, particularly in recombinant protein production. It is a protein rather than a synthetic peptide, which affects how it is made, tested and handled. The intact mass is approximately 9,111 Da and the CAS number is 946870-92-4.
The published literature on the compound, with references, is collected in the monograph.
What you receive
Each vial contains IGF-1 LR3 as a white lyophilised powder, sealed with a flip-off cap over a crimped stopper, in the net quantity stated on the label: 1 mg. The protein is lyophilised from a dilute acid solution and the certificate states whether any carrier or buffer salt is present. The batch number is printed on the label and matches the certificate in our register.
Reading the certificate for an IGF-1 LR3 batch
A recombinant protein is certified a little differently from a synthetic peptide. Purity by reversed-phase HPLC is reported as the area of the main peak against all peaks, and a well-made lot should be above 95%; some laboratories add SDS-PAGE as a second view. Identity is confirmed by electrospray mass spectrometry, where the many charge states of a 9 kDa protein are deconvoluted to an intact mass compared against the expected value of about 9,111 Da. A match confirms the full sequence with the N-terminal extension and that all three disulphide bonds are formed.
Protein content, the counterpart of net peptide content, is usually determined by UV absorbance at 280 nm or by a colourimetric assay and is the figure to use when preparing a stock solution. A correctly folded and a misfolded protein share the same mass, so the HPLC retention time, and where reported a cell-based activity assay, are the checks on folding. Our guide to reading a certificate of analysis walks through annotated examples.
Storage and handling
Sealed vials should be kept at −20 °C and protected from light; 2 to 8 °C is acceptable for short periods. The lyophilised protein is stable for well over a year frozen. Allow the vial to reach room temperature before opening so that condensation does not form on the powder. LR3 IGF-1 is sparingly soluble at neutral pH and is normally reconstituted in dilute acid, for which acetic acid 0.6% is the appropriate solvent, before further dilution into buffer or medium. Reconstituted solutions should be aliquoted and frozen in low-binding tubes, since proteins at low concentration adsorb to plastic; the storage and stability guide covers solvents, concentrations and freeze-thaw behaviour.