Preparation and binding of radioactively labeled porcine transforming growth factor type β

This report describes the labeling of porcine transforming growth factor type β (TGF-β) with ¹²⁵-iodine. Its binding to NRK cells and three other cell lines has been examined. The data indicate that NRK cells exhibit approximately 10,000 receptors for porcine TGF-β per cell, with an apparent dissociation constant of 45 pM. The binding of porcine ¹²⁵I-TGF-β can be blocked by porcine, murine and human TGF-β but not by several well characterized growth factors. In all respects examined, the binding observed with porcine ¹²⁵I-TGF-β appears to be the same as that observed with human TGF-β. The findings reported here argue that porcine ¹²⁵I-TGF-β can be used to quantitate TGF-β receptors on a wide range of mammalian cells.