What Is a Peptide Assay?

C-peptide is a peptide fragment containing 31 amino acids that is cleaved during the conversion of proinsulin into insulin under the action of proteolytic enzymes. Its molecular weight is 3020. Proinsulin includes the A and B chains of insulin , C peptide and a single sequence. C peptide connects insulin A and B chains. In the process of insulin synthesis, a single sequence is cut by a protease, and then C peptide is also removed. The insulin A and B chains are composed of two Sulfur bonds are linked to produce insulin, so C peptide and insulin are released equimolar. On the other hand, C-peptide is not easily degraded by the liver, so measuring C-peptide is measuring the amount of insulin, which can accurately reflect the function of islet cells. All factors that can stimulate or inhibit insulin secretion can affect the release of C-peptide. Therefore, the clinical significance of serum C-peptide measurement is the same as that of insulin measurement, but the half-life of C-peptide is 3 to 4 times that of insulin.