This peptide is from amino acid 3-42 of the full length 42-amino acid long GIP (Glucose-dependent Insulinotropic Polypeptide or also known as Gastric Inhibitory Polypeptide). The in-vivo degradation of the first two N-terminal amino acids (Tyr-Ala) by the enzyme dipeptidyl peptidase IV (DPP IV) results in making GIP (3-42) a potent antagonist as opposed to the agonist full length GIP on the GIP receptor.
Pyroglutamyl (pGlu) peptides may spontaneously form when either Glutamine (Q) or Glutamic acid (E) is located at the sequence N-terminus. The conversion of Q or E to pGlu is a natural occurrence and in general it is believed that the hydrophobic γ-lactam ring of pGlu may play a role in peptide stability against gastrointestinal proteases. Pyroglutamyl peptides are therefore considered a normal subset of such peptides and are included as part of the peptide purity during HPLC analysis.