Elevation of C-peptide immunoreactivity in plasma of normal subjects after trypsin action

After measuring the effects of trypsin on the plasma of forty-five fasting healthy subjects, a very large increase in C-peptide immunoreactivity was observed. Determination of the proinsulin concentration by gel filtration showed that this increase could not be solely imputed to conversion of circulating proinsulin into desalanyl-insulin and C-peptide by trypsin. Consequently, it is suggested that certain plasma proteins structurally similar to C-peptide might be released by the action of trypsin and crossreact in the radioimmunoassay.