What Is Tesamorelin? GHRH Analog Sequence and Molecular Weight

Key takeaways

• Tesamorelin is a synthetic analog of human growth-hormone-releasing hormone, GHRH(1-44), modified for stability rather than a wholly new sequence.
• It is a 44-residue peptide carrying a trans-3-hexenoic acid (trans-hex-3-enoyl) group attached to the N-terminal tyrosine, which is the defining structural difference from native GHRH(1-44).
• The molecular formula is commonly cited as C221H366N72O67S with an average molecular weight near 5135.9 g/mol, making it a large peptide relative to short secretagogues like ipamorelin.
• Research vials ship lyophilized, are frequently supplied as an acetate salt, and are reconstituted with bacteriostatic or sterile water; concentration equals labeled peptide mass divided by diluent volume.
• Ascend Bio Labs supplies research peptides with a public, per-batch COA keyed to the batch ID on each vial, independent third-party HPLC for purity and LC-MS for identity, all US-domestic.

Tesamorelin sits in a different structural category from the short growth-hormone secretagogues it is often catalogued beside. Where ipamorelin is a five-residue synthetic peptide and MK-677 is not a peptide at all, Tesamorelin is a near-full-length analog of a natural hypothalamic releasing factor, modified at one end to resist enzymatic breakdown. This guide stays strictly structural: it covers what kind of molecule Tesamorelin is, the GHRH(1-44) backbone it is built on, the chemical modification that distinguishes it, how its molecular formula and weight are calculated, the salt form you are likely to receive, and the mechanics of reconstituting and storing a lyophilized research vial. Nothing here addresses what the compound does in any organism it is written for laboratory handling and characterization only.

Understanding the structure is also what lets you read a certificate of analysis for the material. The 44-residue sequence plus the N-terminal modification fixes the theoretical mass that LC-MS should confirm; the salt form changes the net peptide content per vial; and the lyophilized presentation dictates how reconstitution math works. Each section below ties a structural fact to the practical handling consequence that follows from it.

Peptide class: a stabilized GHRH(1-44) analog

Tesamorelin belongs to the class of growth-hormone-releasing-hormone analogs. Native human GHRH is produced as a 44-residue peptide, conventionally written GHRH(1-44), and the first 29 residues GHRH(1-29) carry the segment most associated with its receptor-binding activity. Tesamorelin is built on the full 44-residue GHRH backbone rather than the truncated 1-29 fragment, which is the first thing that distinguishes it structurally from shorter GHRH-derived research peptides such as sermorelin, a GHRH(1-29) analog.

The word 'analog' is doing precise work here. Tesamorelin is not a freshly invented sequence; it is the natural GHRH(1-44) primary sequence with a single, deliberate chemical addition at the N-terminus designed to slow enzymatic degradation. In a research-catalogue context, treat 'Tesamorelin' as a label for that defined, modified 44-residue molecule rather than as a description of any biological role.

Because it carries a peptidic backbone of native-type residues plus one acyl modification, Tesamorelin is a genuine large peptide, well above the length of the short synthetic secretagogues. For a contrast in the same functional catalogue category, the five-residue structure of ipamorelin is covered in What Is Ipamorelin? Pentapeptide GH Secretagogue Specs, and the non-peptide alternative in What Is MK-677 (Ibutamoren)? Non-Peptide GH Secretagogue Profile.

• Class: growth-hormone-releasing-hormone (GHRH) analog.
• Built on the full 44-residue GHRH(1-44) backbone, not the 1-29 fragment.
• Modified analog of a natural sequence, not a wholly synthetic novel chain.
• A large peptide relative to short secretagogues like ipamorelin.

The defining modification: an N-terminal trans-3-hexenoyl group

The single structural feature that separates Tesamorelin from native GHRH(1-44) is a chemical group attached to the N-terminal residue. The N-terminus of GHRH(1-44) begins with a tyrosine, and in Tesamorelin that tyrosine carries a trans-3-hexenoic acid moiety the trans-hex-3-enoyl group bonded to its alpha-amino group. This is why Tesamorelin is described as a stabilized or N-terminally modified GHRH analog rather than as plain GHRH(1-44).

The point of this acylation is structural protection. The exposed N-terminus of an unmodified peptide is a recognizable target for aminopeptidase and dipeptidyl-peptidase activity, and capping it with a hydrophobic acyl group is a well-known strategy for slowing that cleavage. The trans-3-hexenoyl cap is the specific implementation chosen for this molecule; it is a six-carbon unsaturated acyl group, and its presence is exactly what an identity check is meant to confirm alongside the rest of the sequence.

From a characterization standpoint, the modification has two consequences. It adds atoms to the molecular formula relative to native GHRH(1-44), shifting the theoretical mass that LC-MS should report. And it slightly increases the molecule's hydrophobicity at the N-terminus, which can subtly affect chromatographic retention an HPLC purity method developed for Tesamorelin is validating this modified molecule specifically, not the unmodified hormone.

• Native GHRH(1-44) begins with an N-terminal tyrosine residue.
• Tesamorelin adds a trans-3-hexenoic acid (trans-hex-3-enoyl) group to that N-terminus.
• The acyl cap is a structural-stability modification, not a sequence change.
• The modification shifts both the theoretical mass and the chromatographic behavior.

The sequence: a 44-residue chain plus a C-terminal amide

The defining feature of any peptide is its primary sequence. Tesamorelin's backbone follows human GHRH(1-44): a single 44-residue chain running from the N-terminal tyrosine to a C-terminal leucine, with the modification described above appended at the N-terminus. Native GHRH(1-44) is amidated at its C-terminus that is, the terminal carboxyl is presented as an amide (-NH2) rather than a free acid and this C-terminal amide is part of the molecule's defining structure.

So two terminal details matter for identity: the N-terminus is acylated with the trans-3-hexenoyl group, and the C-terminus is amidated. Both differ from what you would get by simply synthesizing the bare 1-44 amino-acid string with free termini, and both are encoded into the theoretical mass. A mass-spectrometry identity check on Tesamorelin is validating that the assembled 44-residue chain carries both of these terminal features in addition to the correct residue order.

Because the chain is long and contains a cysteine-free mix of standard residues, Tesamorelin has no disulfide bridges; it is a linear acylated, amidated peptide. A clean purity peak with the wrong mass would indicate a pure but incorrect molecule, which is why a complete certificate reports identity (by LC-MS) and purity (by HPLC) as two separate measurements. For the distinction between those two analyses, see HPLC vs LC-MS Peptide Testing: What Each Measures.

• Backbone: the 44-residue human GHRH(1-44) sequence, N-terminal Tyr to C-terminal Leu.
• N-terminus: acylated with the trans-3-hexenoyl group.
• C-terminus: amidated (-NH2), as in native GHRH(1-44).
• Linear chain with no cysteine residues and no disulfide bonds.

Molecular formula and weight, and why the salt form matters

Summing the 44 residues together with the N-terminal trans-3-hexenoyl modification and the C-terminal amide gives a molecular formula commonly cited as C221H366N72O67S for the free-base peptide. The single sulfur atom comes from the one methionine in the GHRH sequence. The corresponding average molecular weight is approximately 5135.9 g/mol, with the monoisotopic mass slightly lower; you will see small rounding differences between sources depending on whether average or monoisotopic mass is quoted. For research characterization, the figure that matters is that the observed mass on an LC-MS readout should land on the theoretical mass for this formula within instrument tolerance.

At roughly 5.1 kDa, Tesamorelin is a large peptide far heavier than the short secretagogues it is shelved near. The five-residue ipamorelin sits near 700 g/mol, and CJC-1295 (itself a modified GHRH(1-29) analog) is lighter still than Tesamorelin because it is built on the shorter 1-29 fragment. The mass difference is a direct consequence of Tesamorelin retaining the full 44-residue backbone; for the GHRH(1-29)-based comparison, see What Is CJC-1295? GHRH Analog Structure, With and Without DAC.

The salt form is the most common source of confusion about how much peptide is in the vial. Tesamorelin is frequently supplied as an acetate salt, because the acetate or trifluoroacetate counterions used in purification and lyophilization remain associated with the peptide's basic residues. An acetate salt weighs more than the free base for the same number of peptide molecules, so a vial labeled by gross fill weight contains slightly less net peptide than the free-base molecular weight alone would suggest. A rigorous COA may report net peptide content (active weight) separately from gross fill.

• Free-base molecular formula: commonly C221H366N72O67S.
• Average molecular weight: approximately 5135.9 g/mol (monoisotopic slightly lower).
• Roughly 5.1 kDa a large peptide versus short secretagogues.
• Often supplied as an acetate salt, raising the as-weighed mass per vial.

The lyophilized vial and reconstitution math

Research Tesamorelin ships as a lyophilized (freeze-dried) powder or thin cake in a sealed vial, typically under an inert headspace. Lyophilization removes water from the frozen peptide under vacuum, leaving a dry solid that is far more stable in transit and storage than a solution would be. The visible amount of cake can look small a few milligrams of peptide occupy very little volume so do not judge fill weight by eye.

Reconstitution converts the dry vial into a solution of known concentration for laboratory work. The diluent is typically bacteriostatic water (sterile water with a small amount of benzyl alcohol as a preservative) or plain sterile water; bacteriostatic water is common when a reconstituted vial will be drawn from more than once. The diluent is added slowly down the inner wall of the vial rather than directly onto the cake, and the vial is swirled, not shaken vigorously, until the powder fully dissolves. Tesamorelin's larger, more hydrophobic structure means it can dissolve a little more slowly than a small peptide, so allow gentle swirling and time at room temperature.

The resulting concentration is pure arithmetic: it is the labeled peptide mass divided by the volume of diluent you add. Adding 2 mL of water to a 5 mg vial yields 5 mg / 2 mL = 2.5 mg/mL; adding 1 mL to the same vial yields 5 mg/mL. The vial's peptide mass is fixed by what was filled and tested, so the only variable you control is the diluent volume, and that volume sets the concentration. Because the chosen volume drives the math, this peptide reconstitutes by exactly the same procedure as any other lyophilized research peptide for the full step-by-step volume calculation see Reconstituting Lyophilized Peptides: BAC Water Math Step by Step.

• Ships lyophilized in a sealed vial under inert headspace.
• Diluent: bacteriostatic water (multi-draw) or sterile water.
• Add diluent down the vial wall; swirl gently, allow time to dissolve.
• Concentration = labeled peptide mass divided by diluent volume added.

Storage and the per-batch COA

Storage requirements differ sharply between the dry and the dissolved states. As a sealed lyophilized powder, Tesamorelin is comparatively stable and is commonly stored refrigerated, with freezing used for longer-term holding; kept dry, cold, and away from light, a freeze-dried peptide cake is far more forgiving than a solution. The sealed inert headspace and the absence of water are what give the dry form its stability. As a large peptide, Tesamorelin benefits from careful cold, dark, dry storage in particular, since longer chains have more potential sites for degradation.

Once reconstituted, the peptide is in solution and should be treated as the more perishable form: kept refrigerated, protected from light, and used within a limited window. Repeated freeze-thaw cycling of a reconstituted vial is generally avoided because each cycle stresses the peptide; this is one reason bacteriostatic water is chosen for vials that will be sampled multiple times. None of this is a usage instruction it is ordinary cold-chain handling for a research reagent. The general principles are collected in Peptide Storage and Cold-Chain Handling: A Research Reference.

Storage handling and COA both come back to the same principle: the material's identity and quality are established at the batch level and then preserved by correct handling. Ascend Bio Labs supplies research peptides with a public, per-batch certificate of analysis keyed to the unique batch ID printed on each vial, with independent third-party HPLC for purity and LC-MS for molecular identity, and US-domestic synthesis, testing, storage, and shipping with insulated, tracked transit so the dry vial that arrives is the one its certificate describes.

• Lyophilized powder: store cold and dry, away from light; freeze for long-term holding.
• Reconstituted solution: refrigerate, protect from light, use within a limited window.
• Avoid repeated freeze-thaw cycles of a reconstituted vial.
• Batch ID on the vial links the material to its public, per-batch COA.

Related research notes

• What Is CJC-1295? GHRH Analog Structure, With and Without DAC
• What Is Ipamorelin? Pentapeptide GH Secretagogue Specs
• What Is MK-677 (Ibutamoren)? Non-Peptide GH Secretagogue Profile
• Peptide Storage and Cold-Chain Handling: A Research Reference