Degradation of somatomedins by the thioredoxin system

The insulin disulfide reducing thioredoxin system from E. coli was used to investigate a possible mechanism of degradation for the two somatomedins, insulin-like growth factor I and II (IGF-I and -II). The amounts of IGF-I and -II remaining after degradation were measured by use of human placenta radioreceptor assay. The results show that both IGF-I and -II were as sensitive to disulfide reduction as insulin.