Binding, internalization and intracellular processing of 125I-epidermal growth factor purified by isoelectric focusing

When epidermal growth factor (EGF) which had been extensively purified by HPLC was subjected to iodination with sodium ¹²⁵iodide, 5 major species of differing isoelectric points were produced. Some of these species bound to rat fibroblasts with different affinities but were internalized with equal efficiency. Examination of the internalized ¹²⁵I-labelled molecules revealed processing of all the ¹²⁵I-EGF species to macromolecules with more acidic isoelectric points. The ¹²⁵I-EGF species with a pI of 4.5 corresponded in electrofocusing behavior with intact non-iodinated EGF. Other EGF species probably represented molecules which were covalently modified as a result of the iodination procedure.