HGH Molecular Profile: Somatropin Structure, Sequence & Properties

Recombinant human growth hormone (INN somatropin; also written rHGH or rhGH) is the laboratory-produced form of human growth hormone (GH, GH-N, somatotropin). It is a single-chain protein of 191 amino acids manufactured by recombinant DNA technology, and is structurally identical to the 22 kDa growth hormone secreted by somatotroph cells of the anterior pituitary gland.

Research-use-only: This page is a molecular and scientific reference describing the somatropin molecule for Australian researchers. It is provided for laboratory research use only and is not medical advice, a treatment recommendation, or a dosing guide. Endogenous growth-hormone physiology is described here only to characterise the molecule — it is not a claim about how a research vial behaves or should be used.

It is important to separate two things on this page. Endogenous GH is the hormone the pituitary releases in pulses; its physiology (receptor signalling, half-life) is well characterised in the literature. The recombinant research compound is the same 191-amino-acid protein supplied in a vial for laboratory work. This page focuses on the molecule itself — sequence, mass, registry identifiers and signalling. For experimental context see the HGH research guide, and for how it compares with secretagogue peptides see HGH vs CJC-1295/Ipamorelin.

Somatropin is a single-chain polypeptide of 191 amino acids that folds into a four-helix bundle. The mature protein carries two disulfide bonds formed between its four cysteine residues: Cys53–Cys165 (a long-range bond bridging the core) and Cys182–Cys189 (a small C-terminal loop), using the mature-protein numbering.

The verified one-letter sequence of the mature 191-residue chain is:

FPTIPLSRLFDNAMLRAHRLHQLAFDTYQEFEEAYIPKEQKYSFLQNPQTSLCFSESIPTPSNREETQQKSNLELLRISLLLIQSWLEPVQFLRSVFANSLVYGASDSNVYDLLKDLEEGIQTLMGRLEDGSPRTGQIFKQTYSKFDTNSHNDDALLKNYGLLYCFRKDMDKVETFLRIVQCRSVEGSCGF

Because the sequence and disulfide architecture are identical to the 22 kDa pituitary isoform, the recombinant protein engages the growth hormone receptor in the same way the native hormone does — the basis for the signalling described below.

The table below lists the confirmed molecular and identifier data for somatropin (the 191-amino-acid, 22 kDa form). Values are drawn from public protein and chemistry registries; no PubChem CID or UNII is asserted here.

Registry records can be cross-checked on UniProt (P01241) and DrugBank (DB00052). For laboratory handling considerations, refer to the peptide reconstitution and storage guide rather than treating any single figure as a specification.

Human growth hormone exists as more than one isoform. The form described throughout this page — and the form supplied as 191-amino-acid research vials — is the canonical 22 kDa isoform (191 residues, ≈22,125 Da).

A smaller ~20 kDa isoform also occurs in the pituitary. It arises from use of a cryptic splice site within exon 3 that removes residues 32–46 (a Δ32-46 deletion), and represents roughly 5–10% of pituitary GH. It is mentioned here only for completeness: the recombinant research compound in the 191-amino-acid vials is the full-length 22 kDa form, not the 20 kDa splice variant.

The pharmacokinetics summarised here describe endogenous / clinical growth hormone as reported in the literature. They characterise the hormone's behaviour in the body and are not a property or claim about how a research vial is used.

Circulating 22 kDa GH is cleared quickly. After intravenous administration of 22 kDa GH in healthy adults, the elimination half-life is short and diurnally variable — reported at approximately 14 minutes in the morning rising to about 19 minutes in the evening. Summarised broadly, the elimination half-life of GH is on the order of ~10–20 minutes, and depends on context such as time of day and body size. This short, context-dependent half-life reflects endogenous/clinical pharmacokinetics only.

Growth hormone acts through the growth hormone receptor (GHR), a member of the class I (haematopoietin) cytokine receptor family. One GH molecule binds a preformed GHR dimer; the binding event repositions the two receptor chains and their associated kinases rather than recruiting a receptor from scratch.

GHR has no intrinsic kinase activity. Activation brings together the receptor-associated tyrosine kinase JAK2, which trans-phosphorylates and is activated, then phosphorylates tyrosines on the receptor tail. This creates docking sites for STAT5 (and to a lesser extent STAT1 and STAT3), which are phosphorylated, dimerise and translocate to the nucleus. STAT5 drives transcription of GH target genes, prominently IGF-1. GHR/JAK2 also engages the MAPK and PI3K/Akt pathways.

Many of growth hormone's growth-promoting effects are mediated indirectly by IGF-1 (the somatomedin), produced largely in the liver in response to GH — the basis of the somatomedin hypothesis. Metabolic actions of GH on glucose, lipid and protein handling are also well characterised in the literature.

Sources:

• Brooks AJ, Waters MJ. The growth hormone receptor: mechanism of activation and clinical implications. Nat Rev Endocrinol. 2010;6(9):515–525. PMID 20664532.
• Waters MJ, Brooks AJ. JAK2 activation by growth hormone and other cytokines. Biochem J. 2015;466(1):1–11. PMID 25656053.
• Brooks AJ, Dai W, O'Mara ML, et al. Mechanism of activation of protein kinase JAK2 by the growth hormone receptor. Science. 2014;344(6185):1249783. PMID 24833397.
• Le Roith D, Bondy C, Yakar S, Liu JL, Butler A. The somatomedin hypothesis: 2001. Endocr Rev. 2001;22(1):53–74. PMID 11159816.
• Møller N, Jørgensen JOL. Effects of growth hormone on glucose, lipid, and protein metabolism in human subjects. Endocr Rev. 2009;30(2):152–177. PMID 19240267.
• Bartke A, Sun LY, Longo V. Somatotropic signaling: trade-offs between growth, reproductive development, and longevity. Physiol Rev. 2013;93(2):571–598. PMID 23589828.

Continue across the HGH research cluster: HGH research guide, HGH vs CJC-1295/Ipamorelin, HGH vs IGF-1, HGH and body composition, HGH and sleep, and the HGH pharmacokinetics. Research-grade vials: HGH 100IU kit, HGH 240IU kit, and HGH 400IU kit.