Chloroplast derived IGF-1 before and following hydroxylamine treatment. Transgenic tobacco IGF-1 was purified from centrifuged plant homogenates by IgG-sepharose affinity column chromatography. Proteins eluted from the IgG-sepharose column were identified by polyacrylamide gel electrophoresis. Lanes from left to right: molecular weight marker proteins (MW), human insulin like growth factor 1 (human IGF-1), tobacco chloroplast-derived human IGF-1, (IGF-1A). Darker upper broad band of approx. 15 kDa = IGF-1 linked to Staphylococcus aureus Z domains. Partial removal of S. aureus Z domains by hydroxylamine cleavage (IGF-1B), lower broad band = IGF-1. Right lane = human insulin.