Buy FRAGMENT 176-191 2mg

Fragment 176-191 isolates a 16-residue segment from the C-terminus of growth hormone (hGH), a design that lets researchers study this specific region independent of the other functional domains found elsewhere in the full-length hormone.

Structural Rationale for C-Terminal Isolation

The C-terminal domain of hGH is structurally and functionally distinct from the region responsible for stimulating insulin-like growth factor-1 (IGF-1) release, which resides elsewhere in the full-length molecule.¹

By excluding the IGF-1-stimulating domain entirely, Fragment 176-191 allows researchers to study this C-terminal region's signaling in cell-based systems without the confounding variable of concurrent IGF-1 elevation seen with full-length hGH.

Sequence Relative to Related Analogs

Fragment 176-191 reproduces residues 176 through 191 of native hGH, beginning with phenylalanine at the N-terminus. It is distinct from AOD-9604, a related analog that carries tyrosine in that position, and the two compounds differ in molecular formula and mass.

Analytical Documentation for Bulk Quantities

Variation in counterion content, commonly acetate from the HPLC purification process, can affect net peptide content per milligram of lyophilized powder even at a constant purity percentage.

For bulk orders spanning multiple production batches, researchers designing experiments that depend on precise molar concentration are encouraged to consult lot-specific certificates of analysis, which typically report peptide content alongside purity, rather than assuming uniformity across the full order.

Storage and Handling in the Laboratory Setting

The disulfide bond between Fragment 176-191's two cysteine residues is susceptible to reduction under certain storage conditions, particularly with reducing agents or extended exposure to light and elevated temperature.

Lyophilized storage under sub-zero freezer conditions helps preserve this oxidized state, and a bulk order is best split into a handful of smaller sealed vials as soon as it arrives, rather than reopening one large container throughout a series of experiments.

Where the Fragment Sits in the Full Protein

Full-length growth hormone is a 191-residue protein of roughly 22 kDa, folded into a four-helix bundle. Fragment 176-191 represents the final 16 residues of that chain, about 8% of the total sequence, spanning the end of the fourth helix and the short C-terminal tail.

Studying this segment as a standalone synthetic peptide removes the surrounding helical scaffold, so its conformation can differ from its shape within the intact protein.

How the Peptide Is Synthesized

Fragment 176-191 is typically assembled by Fmoc solid-phase peptide synthesis, adding one protected amino acid at a time from the C-terminal phenylalanine. The two cysteines carry protecting groups during chain assembly so their thiols do not react prematurely.

After cleavage from the resin, a controlled oxidation step joins the cysteines into the intramolecular disulfide. Incomplete oxidation, or linkage between two separate chains, are the main side products that purification is designed to remove.

What the Remaining Percentage Represents

The small remainder below the stated purity consists of related peptide species rather than unrelated contaminants. Typical candidates include:

• Deletion sequences missing a single residue
• The reduced, open-chain form with two free thiols
• Disulfide-linked dimers formed between two fragment molecules
• Truncated chains from incomplete coupling steps

Notably, the sequence contains no methionine or tryptophan, two residues frequently responsible for oxidation impurities in other research peptides.

Counterion Forms: TFA and Acetate

Peptides cleaved from synthesis resin are initially isolated as trifluoroacetate (TFA) salts, because TFA is used in both the cleavage step and HPLC purification. Many suppliers then exchange TFA for acetate, a counterion generally considered more compatible with cell-based assay systems.

The counterion form, and any residual TFA level, may be listed on the certificate of analysis for a given lot.

Reading the Mass Spectrometry Data

Electrospray mass spectrometry often detects peptides of this size as multiply charged ions rather than a single peak at the full mass. For Fragment 176-191, the doubly charged ion appears near m/z 900.6 and the triply charged ion near m/z 600.7.

Seeing this pattern on a certificate of analysis is consistent with the expected 1799 g/mol molecular weight.

Planning Bulk Quantities for a Study

Estimating total peptide needs before ordering, by accounting for the number of assays, replicates, and controls planned, helps ensure an entire study can run from a single lot. Building in a margin for repeat runs avoids switching batches partway through a dataset.

Important Notice

This product is intended for laboratory research use (in vitro) only. It is not approved for human use under any circumstances, and has not been evaluated for safety or efficacy in humans.

Product Information

Fragment 176-191 is supplied as a research reagent for laboratory use only, available in bulk quantity.

References

1. Harvey S, Martinez-Moreno CG. Growth Hormone: Therapeutic Possibilities—An Overview. Int J Mol Sci. 2018;19(7):2015.