Metabolic · Proinsulin-derived connecting peptide
Insulin C-peptide
Also known as C-peptide; proinsulin connecting peptide
The 31-residue human proinsulin connecting peptide, used in studies of precursor processing and beta-cell secretion.
- Length
- 31 amino acids in the mature human sequence
- Half-life
- Not well characterised
- Mechanism
- Within proinsulin, the connecting segment supports folding and alignment of the insulin A- and B-chain regions before proteolytic processing releases C-peptide. Isolated C-peptide has been reported to alter calcium and kinase signalling in some experimental systems, but a universally accepted specific receptor has not been established.
- Studied in
- Pancreatic islets, beta-cell cultures, proinsulin-processing systems and selected endothelial or renal cell models are used to study C-peptide release, detection and proposed signalling.
About Insulin C-peptide
C-peptide is the connecting segment within proinsulin, positioned between the future insulin B and A chains. Proinsulin research in the 1960s established its role in the biosynthetic precursor. Proteolytic cleavage at paired basic sites, followed by removal of residual basic residues, generates mature insulin and free C-peptide. The mature human sequence contains 31 residues and no cysteine, so it lacks the disulphide framework characteristic of insulin itself.
In pancreatic beta cells, insulin and C-peptide are generated in equimolar amounts during complete proinsulin processing and are released from secretory granules together. This makes C-peptide useful for studying secretion, although extracellular concentrations also depend on degradation and sampling conditions. Separate experiments have reported membrane-associated binding and intracellular signalling responses. Those findings require careful controls because receptor identity remains unresolved and results vary with cell type and experimental design.
Laboratory notes
- Use species-matched standards for immunoassays; C-peptide sequences differ substantially between species.
- Assess antibody cross-reactivity with intact proinsulin and processing intermediates before interpreting secretion measurements.
- For signalling experiments, check peptide purity and possible insulin contamination, and include a sequence-control peptide.
Storage and reconstitution basics: storage guide.
Questions about Insulin C-peptide
Does free C-peptide contain disulphide bonds?
The mature human sequence contains no cysteine and therefore cannot form intramolecular disulphide bonds.
Does equimolar production imply equal concentrations in culture samples?
Not necessarily. Differential degradation, adsorption, processing efficiency and assay recognition can alter the measured insulin-to-C-peptide ratio.
Is GPR146 an established C-peptide receptor?
GPR146 has been proposed as a participant in C-peptide-associated signalling, but its status as a direct, specific receptor is not conclusively established.
Is Insulin C-peptide for human use?
No. It is supplied strictly for in-vitro laboratory research and is not for human or animal consumption.
Related research peptides
All products are sold for laboratory research use only. Not for human consumption, not a medicine, not for diagnosing, treating or preventing any condition.