Quick answer: AOD-9604 is described as hGH 177-191 with an extra N-terminal tyrosine. The 176-191 fragment is the native stretch. They differ by one residue, so masses are nearly identical and purity alone cannot separate them; the identity line on the certificate has to. All materials are for laboratory research use only.
Why the two names get mixed up
AOD-9604 and "HGH fragment 176-191" are listed side by side in many supplier catalogs, and the descriptions often read as if they were one product. They are close relatives, but they are not the same molecule, and the difference is small enough that it is easy to miss and important enough to matter in a protocol.
This guide explains where both come from, how they differ in sequence, what the published literature actually reports, and what a certificate should confirm. It is background for laboratory research use only and makes no claim about effects in people or animals. For the single-compound view, see the AOD-9604 research overview.
Where the sequence comes from
Human growth hormone (hGH) is a 191-residue protein. Its C-terminal region, roughly residues 177 to 191, became the subject of interest in the 1990s after work at Monash University in Australia on which parts of the hormone carry which activities in cell and rodent models. That work separated the metabolic activity of the C-terminal region from the growth-promoting activity of the full protein, and it led to short synthetic fragments being studied as research tools.
The fragment ends in a stretch containing two cysteines. In the full hormone these two cysteines are linked by a disulfide bond, and the fragments are normally made with that ring closed. A linear, reduced version is a different species and will not behave the same way in assays.
Side-by-side comparison
| Feature | AOD-9604 | HGH fragment 176-191 |
|---|---|---|
| Length | 16 residues | 16 residues |
| Relation to hGH | hGH 177-191 plus an N-terminal tyrosine | Native stretch from position 176 to 191 |
| Disulfide ring | Present between the two cysteines | Present between the two cysteines |
| Primary literature | Heffernan et al., 2001, and related work | Older and thinner; mostly secondary sources |
| Mass difference | Close to the fragment; one residue differs | Close to AOD-9604; one residue differs |
| Key identity check | Measured mass matches AOD-9604 | Measured mass matches the native fragment |
| Listed by V8 | Yes, for research use only | No |
AOD-9604 versus the 176-191 fragment
AOD-9604 is described in the literature as hGH 177-191 with an extra tyrosine added at the N-terminus, giving a 16-residue peptide. The tyrosine was introduced as a modification to the natural fragment. The material sold as "fragment 176-191" is generally described as the native stretch of the hormone, whose first residue at position 176 is a different amino acid. The two peptides therefore share the 15-residue core and differ at the first position.
Because that difference is a single residue, the two peptides have very close molecular masses, and a purity percentage alone cannot tell them apart. If a protocol specifies one, the certificate has to show which one was supplied. Suppliers sometimes use the names loosely, so the identity line on the report matters more than the product title. Details of the synthetic route for AOD-9604 are in AOD-9604 structure and synthesis.
One caution: descriptions of these peptides online vary, and some pages mix up the numbering. Regard sequence statements from supplier pages as claims to verify against the certificate and the primary literature, not as settled fact.
What the published work reports
The main preclinical paper on AOD-9604 is Heffernan and colleagues, published in Endocrinology in 2001. It examined the fragment in obese mice and in mice lacking the beta-3 adrenergic receptor, and compared it with full-length hGH. The paper is the usual starting point because it describes the peptide in a controlled design and discusses the receptor pathway. Anyone reading it should note that rodent results do not transfer to other species, and nothing here is a statement about people.
The literature on the unmodified 176-191 fragment is thinner and older, and much of the commercial discussion of it is not backed by a primary paper. That imbalance is itself useful information: if a design needs a well-documented reference peptide, AOD-9604 has the more traceable record. The AOD-9604 explainer covers the naming and background in more detail.
What a certificate should show
For either peptide, start with HPLC purity, but do not stop there. Because the two differ by one residue, the identity statement is the key line. A good report names the compound exactly, shows the measured mass against the expected mass, and carries a lot identifier and test date that match the vial. If the report only shows a purity percentage and a generic product name, it cannot distinguish AOD-9604 from the fragment.
Ring closure is the second check. A disulfide-bridged peptide and its reduced form differ by about two mass units, which a mass measurement can reveal if the reader knows to look. An endotoxin result and a sterility statement matter when the material is destined for cell work.
Background reading: understanding HPLC purity, how to read a COA and AOD-9604 purity testing. V8 lists AOD-9604 at this product page, and the sourcing checklist is in where to buy AOD-9604. V8 does not list the 176-191 fragment. V8 certificates, where they exist, report HPLC purity and identity, endotoxin and PCR sterility, and this article is general guidance rather than a statement about any particular lot.
Choosing between them for a research design
If the design needs to reproduce or extend published work on the modified peptide, choose AOD-9604. If it needs the native C-terminal sequence as a control, the native fragment is the logical comparator, sourced separately and documented the same way. Using one as a stand-in for the other without saying so makes the results hard to interpret.
For storage, keep sealed powder cold, dry and away from light, and record the date each vial is opened. Details are in AOD-9604 storage. Write the exact compound name, lot, supplier and certificate date in the lab notebook for every vial.
Frequently asked questions
Is AOD-9604 the same as HGH fragment 176-191?
No. They share the 15-residue core, but AOD-9604 is described as having an added N-terminal tyrosine, while the fragment has the native residue at the first position.
Why does the difference matter?
Because the two have nearly identical mass and similar HPLC behavior, a protocol that names one can be filled with the other if the supplier is loose with names.
Can an HPLC purity number tell them apart?
Not reliably. Identity needs a measured mass compared with the expected mass for the named compound.
Does the disulfide bond matter?
Yes. The ring between the two cysteines is part of the intended structure, and the reduced form is a different species.
Where does the sequence come from?
The C-terminal region of the 191-residue growth hormone, roughly residues 177 to 191.
Is there good primary literature on both?
AOD-9604 has a more traceable record, including a 2001 paper in Endocrinology. The native fragment has less.
Does V8 sell the 176-191 fragment?
No. V8 lists AOD-9604 only, for laboratory research use only.
Do rodent results apply to other species?
No. Preclinical results come from specific models and should not be read across.
Does this article describe a use in people?
No. It is background on structure and sourcing. The product is not sold for human or animal consumption.
What should I record for each vial?
The exact compound name, lot identifier, certificate date, supplier, storage conditions and date opened.
References
- Heffernan MA, Jiang WJ, Thorburn AW, Ng FM. Effects of oral administration of a synthetic fragment of human growth hormone on lipid metabolism. Am J Physiol Endocrinol Metab. 2000;279(3):E501-E507.
- Heffernan M, Summers RJ, Thorburn A, et al. The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and beta(3)-AR knock-out mice. Endocrinology. 2001;142(12):5182-5189.