A sensitive radioimmunoassay for human proinsulin, with sequential use of antisera to C-peptide and insulin.
In this assay for immunoreactive human proinsulin (IRPI), it first is separated from plasma by use of an antiserum to human C-peptide. An immunoprecipitate is then formed by using a precipitating antiserum and polyethylene glycol, after which IRPI is dissociated from the antiserum by incubation in warm HCl, pH 2.0. The resulting mixture is assayed for insulin immunoreactivity by a double-antibody tracer-competition method involving incubation for four days with a high-affinity anti-insulin antiserum. Human proinsulin of recombinant-DNA origin is used as the standard. Added C-peptide at supraphysiological concentrations did not interfere with or react in the assay. Human insulin cross reacted by 1.5%. The detection limit for IRPI (2 SD from zero-dose binding) is 3 pmol/L. Proinsulin conversion intermediates are measured nearly as well as intact proinsulin. IRPI concentrations in 10 nondiabetic human subjects averaged 12.0 (SEM 1.6) pmol/L. The ratio of proinsulin to immunoreactive insulin averaged 14.3 (SEM 2.2)%. After intravenous arginine, the increase in proinsulin was less than that of insulin, and it declined more slowly.
D001120:Arginine; D002096:C-Peptide / Q000276:immunology*; D003429:Cross Reactions; D003920:Diabetes Mellitus / Q000097:blood; D006801:Humans; D007106:Immune Sera; D007328:Insulin / Q000276:immunology*; D008433:Mathematics; D011384:Proinsulin / Q000032:analysis*; D011863:Radioimmunoassay
D002096:C-Peptide; D007106:Immune Sera; D007328:Insulin; D011384:Proinsulin; D001120:Arginine