DPP-4

DPP-4 is dipeptidyl peptidase 4, a serine protease also known as CD26. It exists both as a cell-surface glycoprotein (on T lymphocytes, epithelial cells, and many other cell types) and as a soluble form that circulates in plasma. Its catalytic activity is specific: it cleaves N-terminal dipeptides from polypeptide chains whose second residue (position 2) is a proline or an alanine. That substrate specificity is narrow enough to be physiologically meaningful - a handful of signaling peptides in the body happen to have Xaa-Pro or Xaa-Ala at their N-terminus - and broad enough to make DPP-4 a central regulatory node in peptide metabolism. A comprehensive review of DPP-4 biology is Lambeir et al., Crit. Rev. Clin. Lab. Sci. 2003 (NLM 12959468).

Why DPP-4 matters for incretin peptides

The two incretin hormones GLP-1 and GIP both have alanine at position 2 (GLP-1 N-terminus HAEGTF..., GIP N-terminus YAEGTF...) and are therefore substrates for DPP-4. Cleavage of the N-terminal two residues converts each hormone from a full receptor agonist into a much weaker species; for GLP-1, the resulting circulating half-life of the intact hormone is on the order of a minute. DPP-4 is therefore the principal determinant of native incretin pharmacokinetics. Two classes of therapeutics exploit this biology: DPP-4 inhibitors extend the half-life of endogenous incretins by blocking the enzyme, while DPP-4-resistant incretin analogs replace or modify the N-terminal residue so that the analog is no longer a substrate. The enzyme kinetics underlying GLP-1 inactivation are documented in Deacon et al., Diabetes 1995 (NLM 7789648).

DPP-4 in in vitro peptide research

DPP-4 substrate susceptibility is a routine in vitro property for any GLP-1-, GIP-, or PYY-family research peptide. A stability study that incubates the peptide with recombinant human DPP-4 and monitors the disappearance of the intact form by LC-MS is the standard way to quantify this property, typically reported as a first-order rate constant or a half-life in the enzyme-containing matrix. Peptides that show no detectable cleavage over the assay window under defined conditions are reported as DPP-4-resistant. The same assay can be used to screen DPP-4 inhibitors using a standard chromogenic or fluorogenic substrate (e.g., Gly-Pro-p-nitroanilide or H-Ala-Pro-AMC).

How Open Assay handles DPP-4 information

Where DPP-4 susceptibility or resistance is a defining property of a research peptide (for example, distinguishing native GLP-1 from a DPP-4-resistant analog), Open Assay surfaces that fact with a citation to a published in vitro stability study rather than restating a vendor's marketing claim. Where DPP-4 is itself the enzyme under study, listings for recombinant DPP-4 reference their expression system and specific activity.