The AMDM mutants are on the cell surface and bind CNP like WT-GC-B. 293 cells were transiently transfected with plasmids containing green fluorescent protein (GFP), WT-GC-B or the indicated mutants. Cells were incubated for 1 hr at 4°C with 50 pM 125I-CNP in the presence or absence of 1 μM (upper panel) or increasing concentrations (lower panel) of non-radioactive CNP. The cells were rinsed with binding medium to remove non-specific 125I-CNP, removed from the plate with NaOH, and subjected to gamma counting to determine the amount of specifically bound 125I-CNP associated with the cells. The vertical arrows in the bars and symbols represent the SEM where n = 3.