C-Peptide ELISA Kits

C-peptide is produced simultaneously to insulin. They are included in the insulin precursor - proinsulin. In proinsulin, C-peptide is located as if connecting insulin A and B chains. So, it is called "c(onnecting) peptide". C-peptide is released into the blood in approximately equimolar to insulin by the processing of proinsulin, a precursor of insulin. By the measurement of C-peptide concentration in the blood, it is possible to know the insulin secretory potency of pancreatic β cells in the case during insulin administration or insulin antibodies existing.
LBIS C-peptide Mouse or Rat is a sandwich ELISA system for quantitative measurement of mouse or Rat C-peptide specimen. This is intended for research use only.

What is C-peptide?

C-peptide is produced simultaneously to insulin. They are included in the insulin precursor - proinsulin. In proinsulin, C-peptide is located as if connecting insulin A and B chains. So, it is called "c(onnecting) peptide".

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This figure shows the structure of rat proinsulin. The amino acid sequence of insulin is common to rat and mouse, however, however, a little difference in their C-peptides.
In mouse, the amino acid sequences of C-peptides corresponding to insulin I and II are as follows.

evedpqveql elggspgdlq tlalevarq (mouse I, MW 3,122)
evedpqvaql elgggpgagd lqtlalevaq q (mouse II, MW 3,134)

Usefulness of C-peptide measurement

Secretion and blood levels of C-peptide
C-peptide, after being separated from insulin, is also incorporated into secretory granules and released with insulin. It remains in the blood circulation for considerable longer than insulin though its physiological role is not clear.
So, blood C-peptide assay is used to observe biosynthetic and secretory function for insulin. It is also possible to measure C-peptide in the urine as C-peptide is excreted in urine at high concentration that is closely related to the blood level.
By measuring C-peptide, we can estimate insulin secretion in cases when insulin antibody is present in blood.

Estimation of insulin secretion by cultured cells in the presence of exogenous insulin

Measurement of C-peptide is also useful for the estimation of insulin secretion from cultured islet cells, because very often insulin is added to the culture medium exogenously. In such culture system, it is impossible to measure secreted insulin apart from that added to the culture medium. As C-peptide is produced and secreted in equimolar base to insulin, we can estimate the secreted insulin by measuring C-peptide. Deduction of exogenous insulin from the total insulin would be another way to estimate insulin secretion. But it makes big variation and also influence by the ratio of secreted insulin to exogenous insulin. So, the value would not be trustable.
Our C-peptide assay kit recognize the common amino acid sequence to C-peptide I and II, we can estimate total the amount of C-peptides.

Is there any influence of co-existing proinsulin on C-peptide measurement?

Proinsulin is processed by an enzyme at the position where two basic amino acids (K, R) moieties are present side by side as shown by black arrows in the above figure, yielding equimolar insulin and C-peptide. Most proinsulin was processed while it passes Golgi apparatus to secretory granules, however, some remains without processing and present in secretory granules, and secreted into the blood circulation with insulin and C-peptide.
When we measure insulin or C-peptide in the blood, we have to consider that we also measure the amount proinsulin because the structure of proinsulin includes those of insulin and C-peptide, if we ignore the three-dimensional structure.
We examined this possibility, and got the following results.

  • Cross reactivity of rat C-peptide ELISA kit (U-type) to C-peptides, insulin, and proinsulin of various animals

    Species Substance Cross reactivity(%)*
    Rat C-peptide 100
    Insulin Less than sensitivity
    Pro-Insulin Less than sensitivity
    Mouse C-peptide 75
    Insulin Less than sensitivity
    Human C-peptide 85
    Insulin Less than sensitivity
    Pro-Insulin Less than sensitivity
    Pig Insulin Less than sensitivity
    Cow Insulin Less than sensitivity

    *Cross-reactivity was estimated with 3,000 pg/ml of the substance.

  • Cross reactivity of mouse C-peptide ELISA kit (U-type) to C-peptides, insulin, and proinsulin of various animals

    Animals Substances Crossreactivity (%)
    Mouse C-peptide I 100
    C-peptide II 100
    Insulin Less than sensitivity
    Pro-Insulin Less than sensitivity
    Rat C-peptide 90
    Insulin Less than sensitivity
    Pro-Insulin Less than sensitivity
    Human C-peptide 95
    Insulin Less than sensitivity
    Pro-Insulin Less than sensitivity

    *Cross reactivity was estimated at 3,000pg/ml of the substances.

These results clearly show that C-peptide ELISA kits can measure only C-peptides in the presence of proinsulin or insulin in assay samples.

Features

  • Measurement range 46.9~3000 pg/mL
  • Measurable in a short period (5 hours)
  • A minute quantity of sample is measurable (10 μL with a standard method of operating)
  • All reagents are solution types and are ready to use
  • High measurement accuracy and reproducibility

Kit Components

1) Antibody-coated plate (8 x 12) wells/plate 1 plate
2) Standard C-peptide solution (6,000 pg/mL) 500 μL
3) Buffer solution 60 mL
4) Biotinylated anti C-peptide Antibody 100 μL
5) HRP-conjugated streptavidin 100 μL
6) TMB Solution 12 mL
7) Stop Solution 12 mL
8) Wash Solution (x 10) 100 mL
9) Plate Seal 4 seals

Cross-reactivity

  • Cross-reactivity of mouse C-peptide ELISA kit

    Sample Substance Cross reaction (%)
    Mouse C-peptide1 100
    C-peptide2 100
    Insulin Less than sensitivity
    Proinsulin Less than sensitivity
    Rat C-peptide 89
    Insulin Less than sensitivity
    Proinsulin Less than sensitivity
    Human C-peptide 85
    Insulin Less than sensitivity
    Proinsulin Less than sensitivity
    Porcine Insulin Less than sensitivity
    Bovine Insulin Less than sensitivity
  • Cross-reactivity of rat C-peptide ELISA kit

    Sample Substance Cross reaction (%)
    Rat C-peptide 100
    Insulin Less than sensitivity
    Proinsulin Less than sensitivity
    Mouse C-peptide 92
    Insulin Less than sensitivity
    Proinsulin Less than sensitivity
    Human C-peptide 90
    Insulin Less than sensitivity
    Proinsulin Less than sensitivity
    Porcine Insulin Less than sensitivity
    Bovine Insulin Less than sensitivtiy

Assay Procedure

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* Guideline of washing volume: 300 μL/well
**Guideline of shaking: 600-1200 rpm for 10 seconds × 3 times

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For research use or further manufacturing use only. Not for use in diagnostic procedures.

Product content may differ from the actual image due to minor specification changes etc.

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