HGH 191AA is the 191-amino-acid, single-chain form of human growth hormone (somatropin), a protein of roughly 22 kDa. In the body, the anterior pituitary secretes it, and it signals through the growth hormone receptor. In laboratory settings it is studied as a model ligand for class I cytokine receptor activation, for JAK2/STAT5 signalling in cultured cells, and as a reference standard in protein characterisation work. This article summarises its structure, mechanism, published research, laboratory applications and the handling requirements that affect data quality.
What is HGH 191AA?
HGH 191AA is a recombinant form of the principal 22 kDa isoform of human growth hormone, encoded by the GH1 gene. The “191AA” designation refers to the number of residues in the mature chain. It is a globular protein, not a short synthetic peptide, which matters for handling because tertiary structure must be preserved as well as sequence integrity.
The mature sequence begins with phenylalanine-proline-threonine-isoleucine and ends with a C-terminal phenylalanine. The molecule folds into a four-helix bundle with an up-up-down-down topology, stabilised by two intramolecular disulfide bridges. The calculated molecular weight is approximately 22,125 Da. Because the molecule is non-glycosylated, bacterial expression systems can produce it.
Growth hormone was first isolated from pituitary tissue in the mid-twentieth century, and Choh Hao Li and colleagues were central to that early work. Recombinant production followed in 1979, when Goeddel and colleagues reported expressing a hybrid gene, built from chemically synthesised DNA and enzymatically prepared cDNA, in Escherichia coli. The polypeptide produced matched mature human growth hormone in size and immunological properties. That work established the route by which recombinant material, including the 191-residue form, became available for laboratory use.
Researchers will also meet related terms. A 192-residue variant carrying an additional N-terminal methionine arises in some bacterial systems, and a 20 kDa splice isoform lacking a short internal segment exists naturally. Distinguishing these forms is the reason mass spectrometry data are worth requesting with any batch. Writers and suppliers use “HGH 191 AA”, “hGH (1-191)” and “191-amino-acid somatropin” interchangeably, so it is worth confirming exactly what a certificate of analysis describes.
Mechanism of action
Growth hormone acts through the growth hormone receptor (GHR), a single-pass transmembrane protein belonging to the class I cytokine receptor family. The receptor has no intrinsic kinase activity. It relies on JAK2, a tyrosine kinase constitutively associated with its intracellular domain.
The binding mechanism is sequential and has been resolved in structural detail. The hormone carries two distinct receptor-binding sites. Site 1 has the higher affinity and engages a first receptor molecule. Site 2 then recruits a second receptor, producing a ternary complex with one hormone molecule bridging two receptors. This 1:2 stoichiometry was established crystallographically and is a textbook example of ligand-induced receptor dimerisation. A consequence worth noting is that very high ligand concentrations can favour 1:1 complexes at the expense of productive dimers, so dose-response curves in cell-based assays may be bell-shaped.
Dimerisation brings two JAK2 molecules into proximity so that they transphosphorylate one another and the receptor’s cytoplasmic tail. The phosphorylated tyrosine residues become docking sites for signalling proteins, most prominently STAT5 (chiefly STAT5b in hepatic tissue). Phosphorylated STAT5 dimerises, translocates to the nucleus and drives transcription of target genes, including insulin-like growth factor 1 (IGF-1). Parallel branches engage the MAPK/ERK and PI3K/AKT cascades. Negative feedback follows through SOCS family proteins and phosphatases, which makes timing an important variable in any signalling experiment.
The hormone also binds the prolactin receptor, a point that matters when interpreting results in cell lines expressing both receptors. Specificity controls, such as receptor-blocking antibodies or receptor-null lines, are standard practice.
What the research shows
The published literature on growth hormone is vast, and the studies below are selected because they define how the molecule is understood at a structural and biochemical level.
The first concerns receptor recognition. De Vos, Ultsch and Kossiakoff reported the crystal structure of human growth hormone bound to the extracellular domain of its receptor, published in Science in 1992 and resolved at 2.8 Å. The complex contained one hormone molecule and two receptor molecules, and the authors proposed a sequential mechanism of dimerisation that may be central to signal transduction. The abstract is available on PubMed.
The second study addressed cross-reactivity. Somers and colleagues solved the structure of human growth hormone bound to the extracellular domain of the prolactin receptor, published in Nature in 1994. Comparison with the growth hormone receptor complex showed how one hormone can engage two distinctly different receptor surfaces, which explains why the molecule has lactogenic as well as somatogenic binding properties. The record is on PubMed.
The third is the recombinant expression work already mentioned. Goeddel and co-workers constructed a hybrid gene and expressed it in E. coli under lac promoter control, showing that the bacterial product shared size and immunological behaviour with the native hormone. This paper underpins the modern supply of non-pituitary-derived material and remains a standard reference when discussing production systems.
The fourth is an in vivo model study. In 1982, Palmiter and colleagues reported that mouse eggs microinjected with metallothionein–growth hormone fusion genes produced animals that grew markedly larger than controls. This transgenic work was influential because it demonstrated, in a whole-organism model, that growth hormone gene expression alone was sufficient to alter body size. It is cited here as a research-area description only; readers should consult the original Nature paper for methodology, and nothing in it informs human use.
Beyond these landmark studies, current laboratory literature covers JAK2/STAT5 phosphorylation kinetics, receptor trafficking and shedding, growth hormone binding protein biology, and engineered long-acting variants developed for comparative biochemical analysis.
Research applications
In-vitro work with the 191-residue protein falls into several recognisable categories.
Receptor signalling studies form the largest group. Cell lines expressing the growth hormone receptor, whether endogenously or after transfection, are stimulated with the ligand and probed for phosphorylated JAK2 and STAT5 by western blot, flow cytometry or reporter-gene assay. Time-course experiments reveal the activation and desensitisation profile, while mutant receptors help map the contribution of individual tyrosine residues.
Bioassay development is a second area. Proliferation assays using engineered cell lines that depend on growth hormone signalling for survival are used to confirm that a given batch retains biological activity, and not merely the correct mass. Such assays complement analytical methods because a protein can be chemically intact yet conformationally compromised.
Analytical method development is a third. The protein serves as a reference material for reversed-phase HPLC, size-exclusion chromatography, peptide mapping and intact mass spectrometry. Its well-characterised degradation products, including deamidated, oxidised and aggregated species, make it useful for validating stability-indicating methods.
Structural and biophysical work continues as well, including surface plasmon resonance for binding kinetics, circular dichroism for secondary structure and differential scanning calorimetry for thermal stability. Finally, the molecule is used as a comparator when testing biosimilar candidates, antibody cross-reactivity and immunoassay performance.
Purity, storage and handling
Quality control determines whether results from this protein can be trusted. Reversed-phase HPLC is the baseline method for purity assessment, and it should be supported by size-exclusion chromatography because aggregates and dimers may co-elute or be invisible on a single reversed-phase trace. Mass spectrometry confirms the intact mass and distinguishes the 191-residue chain from the 192-residue methionyl variant. Endotoxin testing is relevant for any cell-based work, since lipopolysaccharide contamination can trigger signalling artefacts that mimic or mask genuine receptor-mediated responses.
A batch-specific certificate of analysis matters because proteins vary between production runs far more than small synthetic peptides do. A generic specification sheet cannot show the purity, mass confirmation and aggregate content of the vial actually received. Researchers should look for a batch number that matches the vial label, the analytical method named for each result, the date of testing and the stated storage conditions.
Because degradation accelerates once reconstituted, batch-level HPLC verification matters more here than with more stable peptides. UK laboratories sourcing HGH 191AA should expect a batch-specific certificate of analysis and lyophilised storage at -20°C, and those comparing the best peptides supplier uk can use those same documentation standards as a practical benchmark for any vendor they assess, whether they are buying a single vial or setting up a repeat supply arrangement.
Lyophilised protein is considerably more stable than solution. Unopened vials are generally held at -20°C, with desiccation, and allowed to reach room temperature before opening so that condensation does not introduce moisture. Once reconstituted, the protein is vulnerable to aggregation, deamidation and oxidation of methionine residues, and agitation can promote aggregation at air-liquid interfaces. Vigorous vortexing should therefore be avoided in favour of gentle swirling. Repeated freeze-thaw cycles are best avoided by preparing small single-use aliquots, and reconstituted material is normally kept at 2-8°C for short periods only. Exact stability windows depend on buffer composition and concentration, so they should be taken from the supplier’s batch documentation and verified in-house for critical assays.
Light sensitivity is a secondary but real concern. Prolonged light exposure can contribute to oxidative damage in proteins containing methionine and tryptophan, so storage in amber vials or in the dark is sensible practice. The choice of reconstitution solvent, whether sterile water, a mildly acidic diluent or a buffered solution, should follow the supplier’s guidance and the requirements of the downstream assay.
Frequently asked questions
What does 191AA mean in HGH 191AA?
The “191AA” refers to the 191 amino acid residues in the mature chain of the principal human growth hormone isoform. It distinguishes the full-length 22 kDa protein from the shorter 20 kDa splice variant and from the 192-residue methionyl form sometimes produced in bacterial expression systems.
How should lyophilised HGH 191AA be stored in a laboratory?
Lyophilised protein is typically stored at -20°C in a sealed, desiccated, light-protected container. Vials should reach room temperature before opening to prevent condensation. Reconstituted material is generally held at 2-8°C for short periods, ideally as single-use aliquots, with exact limits taken from the batch documentation.
How is the purity of HGH 191AA verified?
Purity is usually assessed by reversed-phase HPLC, supported by size-exclusion chromatography for aggregates and mass spectrometry to confirm intact mass. Endotoxin testing is added for cell-based work. A batch-specific certificate of analysis should report each result with the method used and the testing date.
Which receptor does HGH 191AA act on in cell-based research?
It binds the growth hormone receptor, a class I cytokine receptor, through two sequential binding sites that produce a 1:2 ligand-receptor complex. This activates JAK2 and downstream STAT5 signalling. It also binds the prolactin receptor, so specificity controls are advisable in cells expressing both.
This compound is supplied for in-vitro laboratory research only. It is not for human or veterinary use, and it must not be administered to people or animals.
