Gel chromatographic separation of human C-peptide and proinsulin

The immunoreactivity of circulating C-peptide is separated into two main peaks on a Bio-Gel column; the faster peak should not be proinsulin but an associated C-peptide without a covalent bond. Proinsulin is in fact eluted in the fraction prior to the faster eluting peak of C-peptide immunoreactivity with 1 M acetic acid as the eluting buffer. Therefore the use of gel chromatography to study C-peptide and proinsulin needs to be carefully re-evaluated, although the method has been established as one of the standard methods.