AOD-9604 and HGH Fragment 176-191 are the same growth-hormone segment in two chemical states: the fragment is the plain C-terminal sequence, while AOD-9604 adds an N-terminal tyrosine and is supplied with its two cysteines closed into a disulfide bridge. The molecular weights make the relationship explicit — 1817.12 g/mol for the fragment against 1815.08 g/mol for AOD-9604, a difference of almost exactly the two hydrogens lost when a disulfide forms. In an AOD-9604 vs HGH Fragment 176-191 comparison, conformation and analytical traceability are the real variables, not sequence.
Both are supplied as lyophilized powder in 5 mg and 10 mg vials with lot-matched HPLC certificates: AOD-9604 and HGH Fragment 176-191, both listed under fat-loss and metabolic peptides. Both are research chemicals for in-vitro and preclinical laboratory work only, and neither is for human or veterinary use.
AOD-9604 vs HGH Fragment 176-191 at a glance
| Attribute | AOD-9604 | HGH Fragment 176-191 |
|---|---|---|
| Relationship | Modified derivative of the fragment | Unmodified parent sequence |
| Sequence origin | hGH 177-191 with an added N-terminal tyrosine | hGH residues 176-191 as numbered in the parent hormone |
| Length | 16 residues | 16 residues |
| Conformation supplied | Cyclised — intramolecular disulfide closed | Linear as synthesised; cysteines free unless deliberately oxidised |
| CAS number | 221231-10-3 | 66004-57-7 |
| Molecular formula | C78H123N23O23S2 | C78H125N23O23S2 |
| Molecular weight | 1815.08 g/mol | 1817.12 g/mol |
| GH receptor activity reported | Not reported to drive GH receptor dimerisation or IGF-1 induction | Same — the growth-signalling domains sit elsewhere in the hormone |
| Primary research readouts | Adipocyte lipolysis and lipogenesis assays; rodent adipose-depot work | The same readouts, plus structure–activity work on the parent hormone |
| Analytical caution | Confirm the oxidised, ring-closed species | Confirm which redox state the lot actually is |
| Research sizes stocked | 5 mg, 10 mg | 5 mg, 10 mg |
| Purity | ≥99% HPLC, MS identity, lot-matched COA | ≥99% HPLC, MS identity, lot-matched COA |
Where both molecules come from
Structure–function work on human growth hormone through the 1980s and 1990s indicated that the hormone's effects on adipose tissue could be traced to its C-terminal region, while the surfaces required for growth hormone receptor dimerisation and downstream IGF-1 induction lie elsewhere in the 191-residue protein. Isolating the C-terminal segment was a way to test that separation directly: if a 16-residue fragment reproduces the adipose-related readouts without the receptor-mediated growth signalling, the two functions are genuinely separable domains rather than a single integrated response.
HGH Fragment 176-191 is that isolated segment. AOD-9604 is the version taken forward for development: adding a tyrosine at the N-terminus and forming the intramolecular disulfide bridge between the two cysteines locks the peptide into the loop conformation the region adopts within the folded hormone, rather than leaving it as a floppy linear chain. Full-length growth hormone itself is a prescription biologic, listed here for reference only as somatropin and never supplied as a research reagent.
The disulfide is the whole comparison
Two cysteines in a short peptide can exist in three practical states: reduced and free, closed into an intramolecular ring, or joined intermolecularly into dimers and higher oligomers. A cyclic peptide and its linear counterpart differ by only 2 Da, which is easy to miss on a mass spectrum read casually, but they can differ substantially in receptor-facing geometry, in aggregation behaviour and in stability.
That is why the AOD-9604 versus fragment question is more analytical than pharmacological. If a laboratory buys the fragment and lets it sit in an oxygen-permeable dilute solution, some proportion will oxidise on its own, drifting toward the AOD-9604-like state without anyone recording it. Conversely, AOD-9604 exposed to a reducing environment — a buffer containing DTT or beta-mercaptoethanol, for example — will open. Any comparison between the two that does not verify the redox state of both materials at the time of use is comparing labels, not molecules.
What the research record actually supports
The reported work on both compounds sits mainly in cell and rodent systems. Adipocyte cultures are the most common setting, with investigators measuring glycerol and free fatty acid release as lipolysis readouts, lipogenic enzyme activity, and in some designs beta-adrenergic pathway involvement. Rodent studies have examined adipose-depot mass and metabolic markers. A recurring framing in that literature is the contrast against intact growth hormone: whether the fragment produces adipose-tissue effects without the insulin-antagonism and IGF-1 elevation associated with the full hormone.
Two caveats belong on any page that describes this literature honestly. First, findings across the fragment literature have not been uniformly consistent, and several groups have reported weaker or absent effects than the earlier reports suggested — that heterogeneity is itself part of why the compounds remain research tools. Second, AOD-9604 has been through investigational clinical evaluation, and results from those regulated programmes describe pharmaceutical-grade product administered under supervision. They say nothing about a reagent vial and are mentioned here only to describe the state of the record.
Which to choose for which research question
Choose AOD-9604 when conformation must be defined
If the experiment depends on a single, reproducible molecular species — a binding study, a structure–activity series, anything where lot-to-lot geometry drift would be fatal — the cyclised material is the better-defined reagent. It is also the correct choice when replicating published AOD-9604 work specifically, since the added tyrosine and the closed ring are part of what was studied.
Choose the fragment when the parent sequence is the point
If the question concerns the native hGH C-terminal region as it exists in the hormone, the unmodified fragment is the more faithful reagent: no extra residue, no imposed modification. It is also the appropriate starting material for a group intending to control the oxidation state themselves, running reduced and oxidised arms in parallel.
Run both when cyclisation is the variable
The pair is an unusually clean two-point series — the same sequence, differing in one added residue and one ring closure. Comparing them side by side is a direct test of how much of the reported activity depends on conformation rather than on primary sequence. Groups extending beyond growth-hormone fragments typically add a mechanistically unrelated metabolic probe such as 5-Amino-1MQ to distinguish pathway-specific effects from general adipocyte responses; our background piece on the lipolytic fragment covers that context.
Handling, reconstitution and storage differences
Both are short, water-soluble peptides and both are far easier to work with than the acylated incretin analogs, but the free thiols make the fragment the more demanding of the two. Sealed lyophilized vials of either are held frozen and brought to room temperature before opening so moisture does not condense on cold powder. Reconstitution is done by running diluent down the vial wall and letting the cake dissolve without shaking.
The fragment's specific requirement is oxygen control. Reduced cysteines oxidise in aerated aqueous solution, faster at neutral to alkaline pH and faster in the presence of trace metal ions, so working solutions are best prepared fresh, kept slightly acidic where the assay permits, and not left standing in a partly filled tube. AOD-9604, already closed, is comparatively indifferent to this but should still be kept out of reducing buffers. Preparing a concentration is a laboratory calculation: a 5 mg vial reconstituted with 2 mL of diluent yields 2.5 mg/mL, or 2,500 mcg/mL, so 0.1 mL contains 250 mcg. Because the two masses differ by only 2 g/mol, mass and molar concentrations are effectively interchangeable between them — a rare convenience in comparative work. See our reconstitution guide and storage guide, and aliquot both so that neither is repeatedly frozen and thawed.
Purity, identity and COA checks
For this pair the certificate matters more than usual, because the two compounds are 2 Da apart and a purity percentage alone cannot distinguish them. Read the mass-spectrometric result carefully against the expected value — 1815.08 g/mol for AOD-9604 and 1817.12 g/mol for the fragment — and regard a monoisotopic figure quoted without stated resolution as insufficient. On the chromatogram, look for an early or late satellite peak of similar area, which in a cysteine-containing peptide often indicates a mixture of redox states, and for high-mass shoulders suggesting disulfide-linked dimer. Confirm the lot number on the certificate matches the vial in hand. Our COA guide explains what a complete document should contain.
Regulatory framing
Both compounds are supplied as research chemicals for laboratory use only. Neither is an approved medicine in the United States; AOD-9604 has been evaluated in investigational settings and also holds food-ingredient status in some jurisdictions, but neither status applies to the reagent supplied here. Full-length growth hormone is a prescription-only biologic and is listed in our catalogue for reference purposes only. Nothing on this page is a protocol for human or veterinary use. For broader context see our metabolic research overview.