Immunologic and Biologic Activities of the Heterogeneous Components of Insulin

Four preparations of crystalline porcine insulin were fractionated into two peaks by Sephadex gel filtration in 1M acetic acid. The minor peak b was of larger molecular size than the major insulin containing peak c. Peak b was heterogeneous on polyacrylamide disc-gel electrophoresis and after limited trypsin digestion a portion migrated on the gels similar to insulin. Peak b had a high degree of cross-reactivity in a radioimmunoassay for porcine insulin. In comparison with its immunoreactivity, peak b had significantly decreased biologic activity as measured by the rat hemidiaphragm and isolated fat cell assays. The possibility that components of peak b may be present in body fluids requires re-evaluation of the biologic effectiveness of substances detected by insulin radioimmunoassay.