Degradation of insulin-like growth factors I and II by a human insulin degrading enzyme.

A human insulin degrading enzyme purified from IM-9 lymphocytes was tested for its ability to degrade insulin-like growth factor I (IGF-I) and insulin-like growth factor II (IGF-II). Degradation of these molecules was assessed by trichloroacetic acid precipitation, binding to specific receptors and chromatography on Sephadex G-50. All three techniques indicated that the enzyme readily degraded IGF-II and slightly degraded IGF-I. The IGF-II degrading activity chromatofocused with the insulin degrading activity and was absorbed by specific antibodies to the insulin degrading enzyme. These studies indicate, therefore, that a human insulin degrading enzyme can degrade IGF-II and, to a lesser extent, IGF-I.