Chevenne D, Letailleur A, Trivin F, Porquet D
Laboratoire de biochimie-hormonologie, hôpital Robert-Debré, Paris, France.
Ann Biol Clin (Paris). 1995;53(1-2):3-9.
Insulin is synthesized from a precursor, proinsulin, then converted in the beta cell by sequential limited proteolysis into insulin and C-peptide, which are stored in secretory granules derived from the Golgi apparatus. Since this process is incomplete, some intact and partially processed proinsulins (split proinsulins) remain trapped in the granules and enter the circulation with insulin and C-peptide. As proinsulins are present in low concentration in serum and show structural homology with insulin and C-peptide, only two-site immunoassays using monoclonal antibodies can achieve sensitive and specific measurements of their intact and split forms. Insulin radioimmunoassays using polyclonal antibodies are not specific since such antibodies cross-react with proinsulins. Two-site immunoassays using monoclonal antibodies improve the specificity and the sensitivity of insulin determination. C-Peptide concentration is measured by radioimmunoassays using polyclonal antibodies which cross-react with proinsulins.
胰岛素由前体胰岛素原合成，然后在β细胞中通过顺序有限的蛋白水解作用转化为胰岛素和C肽，它们储存在源自高尔基体的分泌颗粒中。由于这个过程并不完全，一些完整的和部分加工的胰岛素原（裂解胰岛素原）仍被困在颗粒中，并与胰岛素和C肽一起进入循环。由于胰岛素原在血清中的浓度很低，并且与胰岛素和C肽具有结构同源性，因此只有使用单克隆抗体的双位点免疫测定法才能对其完整形式和裂解形式进行灵敏且特异的测量。使用多克隆抗体的胰岛素放射免疫测定法并不特异，因为此类抗体与胰岛素原会发生交叉反应。使用单克隆抗体的双位点免疫测定法提高了胰岛素测定的特异性和灵敏度。C肽浓度通过使用与胰岛素原发生交叉反应的多克隆抗体的放射免疫测定法来测量。
