INDEX peptide hormones

In the original immunoassay of Yalow and Berson (5), the label of choice was a radioisotope and today radioisotopes are still widely used as labels (see The Immunoassay Index I, Lab. Pract. 32(8) (1983) 21), I being the most commonly used. Radioimmunoassay (RIA) has been used extensively in the determination of steroid and peptide hormones, drugs (both for therapeutic monitoring and for the detection of drugs of abuse) and various macromolecules of clinical interest. 

Insulin [IN suh lin] is a small protein consisting of two polypeptide chains that are connected by disulfide bonds. It is synthesized as a precursor protein (pro-insulin) that undergoes proteolytic cleavage to form insulin and peptide C, both of which are secreted by the p-cells of the pancreas.4 [Note Normal individuals secrete less pro-insulin than insulin, whereas NIDDM patients secrete high levels of the prohormone. Since radioimmunoassays do not distinguish between the two insulin types, NIDDM patients may have lower levels of the active hormone than the assay indicates. Thus measurement of circulating C peptide provides a better index of insulin levels.]... 

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