C-Peptide is a 31-amino acid single-chain peptide that is made when proinsulin is split into insulin and C-Peptide. They split before proinsulin is released from endocytic vesicles within the pancreas-one C-Peptide for each insulin molecule. C-Peptide is the middle segment of proinsulin that is between the N-terminal B-chain (30 amino acids) and the C-terminal A-chain (21 amino acids).
Unlike insulin, C-Peptide has no known physiological function. Due to the fact that C-Peptide has a 2-to-5-time longer half-life than insulin, there are higher concentrations of C-Peptide than insulin in the peripheral circulation. Therefore, plasma C-Peptide concentrations may reflect pancreatic insulin secretion more reliably than the level of insulin itself. C-Peptide is cleared from the body by the kidney, and, unlike insulin, urine concentrations are 20 - 50 times higher than in plasma. Unlike plasma insulin levels, which fluctuate in response to meals, measurement of the 24-hour urinary excretion of C-Peptide provides a useful monitor of average beta cell insulin secretion.
The level of C-Peptide has been used to assess the following clinical applications:
- to assess the residual beta cell function in patients treated with insulin and to distinguish between types 1 and 2 diabetes. Of particular interest is its use to indicate the need for progression to insulin therapy in type 2 diabetes.
- The diagnosis of factitious hypoglycemia. The surreptitious administration of insulin causes high insulin levels in the absence of elevated C-Peptide concentrations.
- Insulinoma diagnosis, especially in patients treated with insulin. C-Peptide measurement is used in insulin suppression tests in euglycemic patients with suspected insulinoma. Elevated C-Peptide levels in this test are indicative of insulinoma.
- As a marker for residual pancreatic tissue after pancreatectomy. In the case of insulinoma, C-Peptide measurement may be used to detect metastasis and the response to therapy. It may also be used to monitor the progress of pancreas or islet cell transplantation
- Strip plates and additional reagents allow for use in multiple experiments
- Quantitative protein detection
- Establishes normal range
- The best products for confirmation of antibody array data
The capture antibody in this kit recognizes the C-Peptide cleavage product of proinsulin produced during production of mature Insulin.
Target Protein Information
Insulin [Cleaved into: Connecting peptide (C-peptide) (CPE)]
- Pre-Coated 96-well Strip Microplate
- Wash Buffer
- Standard Peptide
- Assay Diluent(s)
- Biotinylated Peptide
- TMB One-Step Substrate
- Stop Solution
- Assay Diagram
- Positive Control Sample
- Capture Antibody
- User Manual
Other Materials Required
- Distilled or deionized water
- Precision pipettes to deliver 2 µl to 1 ml volumes
- Adjustable 1-25 ml pipettes for reagent preparation
- 100 ml and 1 liter graduated cylinders
- Tubes to prepare standard and sample dilutions
- Orbital shaker
- Aluminum foil
- Saran Wrap
- Absorbent paper
- Microplate reader capable of measuring absorbance at 450nm
- SigmaPlot software (or other software that can perform four-parameter logistic regression models)
Protocol OutlinePrepare all reagents, samples and standards as instructed.Add 100 µl detection antibody to each well.Incubate 1.5 h at RT or O/N at 4°C.Add 100 µl standard or sample to each well.Incubate 2.5 h at RT.Add 100 µl prepared streptavidin solution.Incubate 45 min at RT.Add 100 µl TMB One-Step Substrate Reagent to each well.Incubate 30 min at RT.Add 50 µl Stop Solution to each well.Read plate at 450 nm immediately.
Standard, Biotinylated C-Peptide peptide, and Positive Control should be stored at -20°C after arrival. Avoid multiple freeze-thaws. The remaining kit components may be stored at 4°C. Opened Microplate Wells and antibody (Item N) may be stored for up to 1 month at 2° to 8°C. Return unused wells to the pouch containing desiccant pack and reseal along entire edge.