Insulin and C-peptide secretion from B cells in human subjects stimulated with glucose

Two groups of immunoreactive insulin in human sera were reported by Kakita et al. (4), using gel chromatography after acid-alcohol extraction. These analogs were noted not only in circulating human sera but also in incubation medium and incubated human pancreas. The release of these insulin analogs was discussed in a previous report (5). The circulating C-peptide immunoreactivity was separated into two groups on a Bio-Gel column, and the early peak should not be proinsulin but an associated C peptide (6). These analogs of insulin were separated by the methods of ion-exchange chromatography, isoelectric focusing, gel electrophoresis, and gel chromatography. Immunoreactive insulin was also separated into two major bands by standard polyacrylamide gel electrophoresis. The fast migrating band corresponds to the rat insulin II position, and the slower corresponds to rat insulin I, which has one more basic amino acid residue in comparison with rat insulin II. Further studies have been performed in five healthy adults in order to elucidate the physiological relationship between analogs of insulin and C-peptide peak substances in human serum; the results are reported in this paper with a consideration of the mechanism of insulin secretion.