HCG, human chorionic gonadotropin, is a heterodimeric glycoprotein hormone produced by placental trophoblast and the reference agonist at the luteinising hormone and chorionic gonadotropin receptor, LHCGR. Its two subunits total 237 residues and heavy glycosylation takes the mass to roughly 36 kDa, which makes it one of the largest and most structurally complex molecules in the research range. NuVion supplies HCG as a laboratory chemical for in vitro research use only.
Key facts
| Type | Heterodimeric glycoprotein hormone |
| Subunits | Alpha (92 residues) and beta (145 residues) |
| Total amino acid count | 237 |
| Molecular weight | Approximately 36 kDa including glycans |
| Carbohydrate content | Around 30 per cent by mass |
| Receptor | LHCGR, a class A G protein-coupled receptor |
| CAS number | 9002-61-3 |
| Supplied form | Lyophilised powder in a sealed vial |
Structure and chemistry
HCG is a non-covalent heterodimer. The alpha subunit of 92 residues is shared with luteinising hormone, follicle-stimulating hormone and thyroid-stimulating hormone, so specificity comes entirely from the beta subunit. The beta subunit of HCG has 145 residues and differs from that of luteinising hormone chiefly by a 24-residue C-terminal extension carrying four O-linked glycans. Both subunits adopt the cystine knot fold, with five disulfide bonds in alpha and six in beta, and the two chains wrap around one another in an elongated arrangement with the beta subunit’s seatbelt loop latching over the alpha subunit.
Glycosylation is roughly thirty per cent of the mass and is not decoration. The N-linked glycans at two sites on each subunit are required for correct folding and for productive signalling, and the O-linked glycans on the C-terminal extension slow clearance from circulation. Because glycan structures vary with the expression system, preparations from different sources differ in charge and in apparent mass on gel, and isoelectric focusing typically shows a ladder of glycoforms instead of a single band. That heterogeneity is normal for the molecule and is why identity confirmation uses immunoassay and intact mass ranges alongside chromatography.
The dimer is held together non-covalently, so the practical stability question is dissociation, not peptide bond cleavage. Subunit dissociation is favoured by low pH, by heat and by air-liquid interface stress from vigorous mixing, and the free subunits are inactive at the receptor. Freeze-thaw and foaming are therefore the main handling risks, and they are the reason solutions are swirled and never shaken.
Mechanism of action
HCG binds the extracellular leucine-rich repeat domain of LHCGR with high affinity, in the picomolar range, which makes it the standard reference ligand for that receptor. Binding rotates the hinge region and activates the seven-transmembrane core, coupling principally to Gs. Adenylyl cyclase activity rises, cyclic AMP accumulates and protein kinase A is activated, and at higher occupancy the receptor also recruits Gq and raises intracellular calcium through phospholipase C. Beta-arrestin recruitment follows, giving receptor internalisation and a distinct pool of signalling from the endosome, which is one reason the receptor is used as a model in studies of sustained versus transient cyclic AMP signalling.
Downstream of protein kinase A, the canonical readout in gonadal cell culture is steroidogenesis. Phosphorylated CREB drives transcription of steroidogenic acute regulatory protein, which moves cholesterol into the mitochondrion, and of the cytochrome P450 side-chain cleavage enzyme that converts it to pregnenolone. In Leydig cell lines the measured output is testosterone in conditioned medium; in granulosa cell models it is progesterone and oestradiol. Because the receptor is well characterised and the ligand affinity is high, the system is widely used as a positive control for Gs-coupled receptor pharmacology and to benchmark cyclic AMP assay performance.
Research applications
- Cyclic AMP accumulation assays in LHCGR-expressing cell lines by HTRF, AlphaScreen or reporter, as a reference agonist for Gs-coupled signalling.
- Steroidogenesis assays in Leydig or granulosa cell culture, quantifying steroid output in conditioned medium by ELISA or LC-MS.
- Radioligand and fluorescent competition binding at LHCGR to determine affinity for test compounds.
- Receptor internalisation and beta-arrestin recruitment assays by imaging or BRET.
- Glycoform characterisation by isoelectric focusing, lectin blot and intact mass analysis.
- Subunit dissociation and stability studies by native gel or size exclusion chromatography under varied pH and temperature.
HCG sits in NuVion’s Reproductive Signalling category alongside the other compounds used in gonadal axis research.
Handling in the laboratory
HCG is supplied lyophilised and is reconstituted with bacteriostatic water added slowly down the side of the vial, then swirled gently until dissolved. It is not shaken or vortexed, because the dimer dissociates at an air-liquid interface and the free subunits do not activate the receptor. The reconstitution calculator converts vial content and diluent volume into a stock concentration. A carrier protein such as bovine serum albumin is often added to dilute working solutions, since a glycoprotein at picomolar working concentration otherwise adsorbs to tube and plate surfaces.
Unopened vials are kept sealed, dry and refrigerated as stated on the product documentation. Reconstituted solution is refrigerated and used within the period given there, or aliquoted into single-use volumes and frozen, because repeated freeze-thaw drives dimer dissociation more than it does simple peptide degradation. Activity is confirmed functionally where it matters, by running a cyclic AMP concentration-response on a receptor-expressing line, since a preparation can pass a mass check while having lost dimer integrity.
Testing and supply from NuVion
NuVion’s HCG is manufactured at a GMP-audited facility and independently tested by Janoshik Analytical, with purity determined by RP-HPLC and identity confirmed by mass spectrometry. The Certificate of Analysis for a tested batch is published on the product page and in the COA library. It is supplied lyophilised in sealed vials and dispatched from within Australia.
Related compounds
Other compounds used in reproductive axis research include Kisspeptin, the ligand at KISS1R upstream of GnRH release, and Oxytocin, the reference ligand at OXTR. Upstream of the gonadotropins, gonadorelin covers the hypothalamic decapeptide that governs their release.
Frequently asked questions
What is HCG used for in research?
It is the standard reference agonist at LHCGR, used in cyclic AMP accumulation assays, in competition binding to determine affinity for test compounds, in steroidogenesis assays on Leydig and granulosa cell culture, and in receptor internalisation and arrestin recruitment work.
Why does HCG need gentle handling?
It is a non-covalent heterodimer, so the practical failure mode is the two subunits coming apart. Shaking, foaming, heat, low pH and repeated freeze-thaw all promote dissociation, and the separated subunits do not activate the receptor even though the total mass in the vial is unchanged.
Is HCG a therapeutic good in Australia?
No. NuVion’s HCG is a laboratory chemical for in vitro research. It is not included in the Australian Register of Therapeutic Goods, has not been assessed by the Therapeutic Goods Administration, and is not for human or veterinary use.
How should HCG be stored?
Lyophilised vials are kept sealed, dry and refrigerated per the product documentation. Reconstituted solution is refrigerated and used within the stated period, or aliquoted into single-use volumes and frozen. Working dilutions usually include a carrier protein to limit adsorption.
Research use only. This product is a laboratory chemical supplied for in vitro research. It is not included in the Australian Register of Therapeutic Goods and has not been assessed by the Therapeutic Goods Administration for quality, safety or efficacy. It is not for human or veterinary use, and nothing on this page is a representation about therapeutic use.
