Epo (R103A) inhibits ¹²⁵I-Epo binding.

¹²⁵I-Epo (at a final concentration of 0.132 nM) was incubated with 32D/EpoR WT cells in the presence of increasing amounts of unlabeled Epo (R103A). Total cell-associated ¹²⁵I-Epo was measured. Binding in the presence of 3000-fold excess unlabeled Epo (to determine nonspecific binding) is shown in the solid circle. Determinations were done in quadruplicate with SD shown.