Assessment of the predicted ET-1/AngII receptor ET-1 binding domain via site-directed mutagenesis. Saturation binding curves with 125I-AngII (A, C, E) and 125I-ET-1 (B, D, F) in the wild-type (W.T.) (A, B), R64G (C, D), and W65G (E, F) ET-1/AngII receptors expressed in permanent Cosl cell transfectants. Mutagenesis and binding studies were performed as described in Materials and Methods. Each curve is representative of at least three independent experiments performed in quadruplicate.