"Immunoreactive dynorphin" in Escherichia coli: tracer degradation by a heat-stable endopeptidase

Escherichia coli cells contain and secrete into the growth medium a heat-stable tryptic enzyme, which degrades the radiolabeled dynorphin tracer peptide during radioimmunoassay, simulating the presence of "immunoreactive dynorphin". The validity of an immunoassay procedure, in each new application, must remain in doubt until tracer integrity has been proved.