Separation and quantitation of serum proinsulin and proinsulin intermediates in humans

Two reversed-phase high-performance liquid chromatographic (RP-HPLC) systems were developed for the separation of human insulin, proinsulin and the major proinsulin intermediates. The individual components were quantified using two enzyme-linked immunosorbent assays for insulin and proinsulin immunore-active material (PIM) after (passive) evaporation of the organic modifier. Serum samples from normal subjects and patients with non-insulin-dependent diabetes mellitus were immunopurified and analysed in one of the RP-HPLC systems. The proportion of PIM relative to insulin immunoreactive material was higher in the diabetic patient compared with that in the normal subject. In both, PIM was heterogeneous, consisting of intact proinsulin and des-proinsulin intermediates.