Rate of binding of ¹²⁵I-labeled rGCR to rat alveolar macrophages at 37°C. Binding of ¹²⁵I-labeled rGCR to rat alveolar macrophages was measured at early time points as described in Materials and Methods. Binding of the radiolabeled enzyme was performed in the presence (⧫) and absence (▪) of yeast mannan. Specific binding (▴) of the enzyme to mannose receptors was calculated from these data.