# H-Frag

> Research use only. Not for human or veterinary use. Supplied by Veracue Labs.

- Page: https://veracuelabs.com/product/h-frag
- Category: GLP-1 & Metabolic
- Sizes and prices in USD: 5 mg at $54.99
- Certificate of analysis: none posted on the page. Request one for a specific lot at https://veracuelabs.com/contact-us.
- Prices are a snapshot from 2026-10-17. The product page shows the current price.

## Overview

H-Frag, also written HGH Fragment 176-191, is a synthetic 16-residue peptide with the sequence FLRIVQCRSVEGSCGF, copied from the closing stretch of the 191-residue human growth hormone chain. Its two cysteines form a disulfide ring, giving the free peptide the formula C78H123N23O22S2, an average mass of 1799.1 g/mol and CAS 66004-57-7. It begins with phenylalanine, which separates it from AOD 9604, whose first residue is tyrosine and whose mass sits near 1815.1 g/mol.

## Product Details

### What Is H-Frag?

H-Frag is the short name for HGH Fragment 176-191, a synthetic peptide of sixteen amino acids copied from the C-terminal end of human growth hormone. Counting from the first residue of the mature hormone, positions 176 to 191 read Phe-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe, or FLRIVQCRSVEGSCGF in one-letter code. The two cysteines, positions 7 and 14 of the peptide and 182 and 189 of the hormone, are joined by an intramolecular disulfide bond.

The same material turns up as H Frag, HGH Frag, hGH Fragment 176-191, Fragment 176-191 and GH Fragment 176-191. All of these point at one native, unmodified sequence. Veracue supplies it as a single defined compound for research use only.

### H-Frag Reference Data

Product name: H-Frag (also H Frag, HGH Frag, hGH Fragment 176-191)
Peptide length: 16 residues, linear sequence with one internal disulfide ring
Sequence: Phe-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe (FLRIVQCRSVEGSCGF)
Source segment: Residues 176 to 191 of mature human growth hormone
Disulfide bond: Cys7 to Cys14 of the peptide (Cys182 to Cys189 of the hormone)
Chain ends: Free N-terminal amine and free C-terminal carboxylic acid
Molecular formula (free peptide): C78H123N23O22S2
Molecular weight (average): About 1799.10 g/mol
Monoisotopic mass: About 1797.87 Da
CAS Registry Number: 66004-57-7
Size offered: 5 mg vial
Research designation: Research Use Only

Formula and masses are reference values for the free peptide with its disulfide intact, and they follow directly from the sequence. They describe the molecule rather than a specific lot. The chemical form, purity, lot number and storage conditions for a particular vial are reported on its own documentation, which you can request through the contact page.

### What H-Frag Is Not

- Not AOD 9604. That peptide opens with tyrosine instead of phenylalanine and has its own formula, mass and CAS number.
- Not full-length growth hormone, which is a 191-residue protein.
- Not a blend or a multi-peptide product.
- Not a consumer, dietary or cosmetic product, and not intended for human or veterinary use.

## Research Focus & Mechanism Overview

### Structure of the Peptide

### What does the H-Frag sequence contain?

Phenylalanine, arginine, valine, cysteine, serine and glycine each appear twice in the chain, while leucine, isoleucine, glutamine and glutamic acid appear once. Two arginines against a single glutamate leave the peptide mildly basic, with a net charge near +1 at neutral pH once the free amine and free carboxylate at the two ends cancel each other. There is no lysine, proline, histidine, methionine, tryptophan or tyrosine anywhere in the sequence.

### What does the disulfide bond do to the molecule?

The Cys7 to Cys14 bridge closes eight residues, Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys, into a ring. That leaves Phe-Leu-Arg-Ile-Val-Gln trailing at the front and Gly-Phe at the back. In the intact hormone the same two cysteines, numbered 182 and 189, form its C-terminal disulfide. For analysis the ring has a practical consequence: a closed peptide is two hydrogen atoms lighter than the open-chain form, so a reading near 1801.1 instead of 1799.1 points to a ring that has been reduced.

### Why does 176-191 describe sixteen residues when 177-191 is only fifteen?

The numbers are residue positions in the mature hormone, counted from 1 to 191, and both ends are included. Positions 176 through 191 therefore make sixteen residues, and the shorter 177-191 stretch starts at leucine. Because position 176 is phenylalanine, the first letter of the sequence is the quickest identity check for H-Frag.

### H-Frag and AOD 9604: Related but Different

Listings frequently treat H-Frag and AOD 9604, also written AOD-9604 or AOD9604, as one compound. They share fifteen residues, yet they are two molecules with separate records.

Feature: H-Frag: AOD 9604

First residue: Phenylalanine: Tyrosine
Sequence: FLRIVQCRSVEGSCGF: YLRIVQCRSVEGSCGF
Hormone positions covered: 176 to 191, unmodified: 177 to 191, with an added N-terminal tyrosine
Disulfide bond: Cys7 to Cys14: Cys7 to Cys14
Molecular formula (free peptide): C78H123N23O22S2: C78H123N23O23S2
Average mass: About 1799.10 g/mol: About 1815.1 g/mol
Monoisotopic mass: About 1797.87 Da: About 1813.86 Da
CAS Registry Number: 66004-57-7: 221231-10-3

The whole difference is one hydroxyl group on the aromatic ring at the first position. That adds a single oxygen atom and about 16 Da, a gap that a mass spectrometer resolves easily, which is why a lot’s measured mass settles the question better than any product name. Findings reported for one peptide should not be carried over to the other.

### H-Frag and Full-Length Growth Hormone

Feature: H-Frag: Full-length growth hormone

Length: 16 residues: 191 residues
Share of the hormone chain: About 8 percent, positions 176 to 191: The complete chain
Structure: Short peptide closed by one disulfide ring: Folded protein
Relationship: Segment copied from the C-terminal end: The parent protein that segment comes from

A sixteen-residue peptide is not a scaled-down copy of the hormone, and a result obtained with the intact protein tells you nothing automatic about the fragment. Whenever results are compared, name the exact material by sequence or CAS number.

### Keeping Research Records Clear

Because HGH Fragment 176-191 and AOD 9604 are confused so often, write the sequence, formula and measured mass next to the product name in any methods note. Veracue offers molecular reference information only, and gives no dosing, administration or usage guidance of any kind.

## Quality & Purity Standards

### Telling H-Frag From Look-Alike Material by Mass

For a peptide this small, identity comes down to mass. Reverse-phase HPLC reports how much of a sample elutes as one main peak, but a clean peak does not say which molecule it is. Mass spectrometry does, and the expected values for H-Frag are easy to tabulate next to its two nearest neighbors.

Species: Average mass (g/mol): Monoisotopic mass (Da): [M+2H]2+ (m/z): [M+3H]3+ (m/z)

H-Frag, disulfide closed: 1799.10: 1797.87: 899.94: 600.30
H-Frag, ring opened (reduced): 1801.12: 1799.88: 900.95: 600.97
AOD 9604, disulfide closed: 1815.10: 1813.86: 907.94: 605.63

Electrospray spectra usually show multiply charged ions rather than the neutral mass, so convert an observed m/z back to a neutral mass before comparing it with the table. A shift of about 2 Da suggests the ring has opened, and a shift of about 16 Da suggests the tyrosine analogue. A single number is a pointer, not a verdict, and tandem MS fragment data that place the first residue add the sequence evidence.

Neither the HPLC trace nor the mass alone describes a lot completely. Together they tell a researcher what the main component is and how much of the detected material it accounts for.

### Reading an H-Frag Certificate of Analysis

A certificate speaks for one lot only, so begin by checking that its lot number matches the vial and your order record. Then look for these items.

- The sequence or CAS number. FLRIVQCRSVEGSCGF and CAS 66004-57-7 belong to H-Frag, while YLRIVQCRSVEGSCGF and CAS 221231-10-3 belong to AOD 9604.
- An observed mass near 1799.1 (average) or 1797.9 (monoisotopic) for the closed free peptide.
- The stated chemical form. A salt or counterion adds mass, so the expected figure moves with the form.
- An HPLC result with its chromatogram, the test date and the testing laboratory.

Results, form and storage conditions are reported on each lot’s own documentation, and the certificate page explains how to request it.

### Verification Questions

### Why can a catalog entry for CAS 66004-57-7 carry a different mass?

Registry numbers are filed under named substances, and some catalog entries attach this number to a salt-form name such as the trifluoroacetate rather than to the free peptide. A salt adds mass, so a lot reported as a salt will not read 1799.1. Compare the observed mass with the expected mass for the form the document states.

### Does a high purity figure show that the vial holds H-Frag?

No. Purity and identity are separate measurements, and a sharp HPLC peak can belong to a closely related peptide. Look for a purity figure and a mass result from the same lot, reported side by side.

### What should a record for this peptide include?

Keep the sequence or CAS number printed on the document, the observed mass, the stated form, the lot number and the receipt date. With those fields on file, a mix-up between H-Frag and its tyrosine analogue would show up at once.

### Need documentation for a specific H-Frag lot?

Ask the Veracue team about the paperwork available for a lot, or browse the published certificates.

- Request lot documentation
- View certificates
- Browse the research catalog

## Compliance Notice

### Research Use Only Notice

H-Frag is supplied for laboratory research and analytical characterization only. It is not intended for human or veterinary use, and it is not a drug, dietary supplement, cosmetic or food. Veracue provides no dosing, administration or usage guidance of any kind. Buyers must be qualified researchers or institutions and must handle the material in line with all applicable laws. See the Medical Disclaimer and the Terms and Conditions for sitewide policies.

### What the Listing Establishes

The identity information here, covering sequence, ring structure, formula, mass and CAS number, describes the H-Frag molecule in general. It cannot establish the purity, content or chemical form of any single vial. Those facts come only from the documentation issued for that lot, which is why certificate checks are always tied to a lot number.

H-Frag is also not a substitute for any other growth hormone fragment. Each related peptide has its own sequence and records, and each should be sourced and documented under its own name.

## Questions and answers

### What is H-Frag?

H-Frag is a synthetic 16-residue peptide that copies positions 176 to 191 of human growth hormone, the end of its C-terminal tail. It is also called HGH Fragment 176-191, and Veracue supplies it for laboratory research only.

### What is the amino acid sequence of H-Frag?

Phe-Leu-Arg-Ile-Val-Gln-Cys-Arg-Ser-Val-Glu-Gly-Ser-Cys-Gly-Phe, written FLRIVQCRSVEGSCGF. The two cysteines at positions 7 and 14 are joined by a disulfide bond.

### What do the numbers in 176-191 mean?

They are residue positions in the mature growth hormone chain, which runs from 1 to 191. Both ends count, so the segment holds sixteen residues.

### What are the molecular formula and mass of H-Frag?

The free peptide with its disulfide closed is C78H123N23O22S2, with an average mass of about 1799.10 g/mol and a monoisotopic mass of about 1797.87 Da. A salt form weighs more.

### What is the CAS number for H-Frag?

The CAS Registry Number is 66004-57-7. Some catalog entries attach it to a salt-form name, so check which form a lot document describes.

### Is H-Frag the same as AOD 9604?

No. AOD 9604 begins with tyrosine where H-Frag begins with phenylalanine, which raises the formula to C78H123N23O23S2 and the mass to about 1815.1 g/mol. Its CAS number is also different, 221231-10-3.

### How can mass spectrometry tell H-Frag from AOD 9604?

The two differ by one oxygen atom, about 16 Da. A lot reading near 1799.1 matches H-Frag, and one reading near 1815.1 matches AOD 9604.

### How is H-Frag different from full-length growth hormone?

Growth hormone is a folded protein of 191 residues. H-Frag is only the last sixteen of them, so it is a different molecule rather than a smaller version of the same one.

### What does the disulfide bond in H-Frag connect?

It links Cys7 and Cys14 of the peptide, which are Cys182 and Cys189 in the full hormone. The bond closes an eight-residue ring in the middle of the chain.

### What size does Veracue offer?

H-Frag is offered as a 5 mg vial, supplied for laboratory research use only.

### What should an H-Frag certificate of analysis show?

A lot number that matches the vial, the sequence or CAS number, the stated chemical form, an observed mass near 1799.1 for the closed free peptide, an HPLC result with chromatogram, the test date and the testing laboratory.

### What does Research Use Only mean?

The material is sold only for laboratory research and analysis, not for human or veterinary use.

### Does Veracue provide usage instructions for H-Frag?

No. H-Frag is offered for laboratory research use only, and Veracue provides no dosing, administration or usage guidance of any kind.

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