GLP-1, GIP and Glucagon Receptor Agonist Peptides: Single, Dual and Triple Agonists Explained for the Laboratory

What "incretin" and "GLP" mean#

GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) are gut-derived peptide hormones. Both belong to the incretin family and act on class B G-protein-coupled receptors (GLP-1R and GIPR). Glucagon is a 29-amino-acid pancreatic peptide that acts on a third, closely related receptor (GCGR). The three receptors share enough structural similarity that a single engineered peptide can be designed to activate more than one of them.

Native GLP-1 has a circulating half-life of about two minutes because the enzyme DPP-4 cleaves its N-terminus. Nearly every research peptide in this class is therefore a modified analog, not the native hormone.

Single, dual and triple agonists#

Single agonists are GLP-1 analogs with substitutions that resist DPP-4 cleavage (for example an Aib residue at position 2) and, in later generations, a fatty-acid side chain that binds albumin and extends the half-life to days.

Dual agonists such as Tirzepatide are 39-amino-acid peptides built on a GIP backbone with GLP-1R activity engineered in. Tirzepatide carries a C20 fatty diacid attached through a linker at lysine 20, which is what gives it its extended pharmacokinetics in the published animal and human pharmacology (Coskun et al., Molecular Metabolism, 2018).

Triple agonists add glucagon receptor activity. GLP-3-R (development code LY3437943) is a single peptide engineered for balanced activity at all three receptors, with a C20 fatty diacid for albumin binding. Its receptor pharmacology was characterized in cell-based assays and rodent models (Coskun et al., Cell Metabolism, 2022). It remains an investigational compound; it is not approved by any regulator for any use.

Why the structure matters on the bench#

Three features of this class decide how the material behaves in a laboratory:

1. Lipidation. The fatty-diacid side chain makes these peptides amphipathic. They are less soluble in plain water than short unmodified peptides and can adsorb to plastics. Assay buffers with carrier protein or appropriate surfactant are the norm in the published methods.
2. Molecular weight. Tirzepatide has a molecular weight of about 4,814 g/mol; GLP-3-R is in the same range. On a mass-spectrometry identity test, the observed mass must match the calculated mass of the modified peptide, side chain included, not the bare sequence.
3. Receptor assays. Potency in this class is reported as EC50 values for cAMP accumulation in cells expressing each receptor separately. A compound described as a "balanced" triple agonist is one whose EC50 values at the three receptors fall within a defined ratio of one another in those assays.

What to check on a COA for a lipidated GLP-class peptide#

• Identity by mass spectrometry. The report should state the observed mass and the calculated mass for the full, lipidated structure. A mass that matches only the unmodified sequence indicates the wrong material.
• Purity by HPLC. Lipidated peptides elute late and can show closely spaced impurity peaks (oxidized methionine, deamidation, truncated side chain). A report that lists the column, gradient and detection wavelength is more useful than one that lists a single percentage.
• Net peptide content. Lyophilized vials contain counter-ions and water as well as peptide. For a 10 mg or 30 mg vial, the mass of peptide is lower than the gross powder mass; a report that states net content lets a laboratory calculate actual molar quantities.
• Lot number on the vial and on the report. They must match. Renuvia Labs publishes each lot's report in the COA library as it is received and shows "Batch report pending" until then.

Regulatory status, stated plainly#

• Tirzepatide is the active ingredient of two FDA-approved prescription medicines (Mounjaro and Zepbound). Research-grade Tirzepatide is not either product and is not interchangeable with them.
• GLP-3-R / LY3437943 is an investigational compound in clinical development by Eli Lilly. It is not approved anywhere.
• Neither compound is a dietary supplement, and no research peptide is a substitute for a prescription medicine. Material sold by Renuvia Labs is for in-vitro and non-human laboratory research by qualified researchers only.

Related reading#

• How to read a Certificate of Analysis
• HPLC and mass spectrometry explained
• Product pages: GLP-3-R · Tirzepatide