The use of reversed-phase high-performance liquid chromatography to detect proteolytic activity from human pancreas in a radioimmunoassay for corticotrophin-releasing factor.

Abstract

Degradation of tracer during a radioimmunoassay (RIA) can result in false-positive concentrations of immunoreactivity being reported in a biological sample. A technique has been developed using reversed-phase high-performance liquid chromatography (HPLC) to detect proteolytic degradation of corticotrophin-releasing factor-41 (CRF-41) during incubation with tissue extracts under RIA conditions. Human pancreatic tissue was extracted in HCl or urea and incubated with 125I-labelled CRF-41 at neutral pH for 18 h. When samples were analysed by HPLC and fractions counted for radioactivity, tracer was extensively degraded. Heating extracts at 85 degrees C or adding lima bean trypsin inhibitor to the medium prevented degradation. Pancreatic tissue extracted in HCl was analysed by gel filtration and HPLC, and fractions were subjected to RIA for CRF-41. A peak of immunoreactivity was detected by both chromatographic methods. However, when this material was incubated with tracer and analysed by HPLC, the tracer was degraded, indicating that proteolytic activity remained after acid extraction and two forms of chromatography.