Prothymosin alpha receptors on peripheral blood mononuclear cells

125I-Labeled prothymosin alpha (ProT alpha) was used to study the presence and characteristics of receptors for ProT alpha on human peripheral blood mononuclear cells (PBMC). The kinetics of 125I-ProT alpha binding to PBMC was fast at 37 degrees C, whilst it required 50 min to reach equilibrium at 4 degrees C and room temperature. Analysis of steady state binding data by the method of Scatchard and by unlabeled ProT alpha competition experiments identified two binding sites with an apparent equilibrium dissociation constant of 216-321 pM for the high-affinity receptor and of 11.4-21.1 nM for the low-affinity one; the sites per cell ranged from 1,479 to 1,519 and from 47,547 to 56,169, respectively. The kinetically derived equilibrium dissociation constant agreed with these data and showed no interaction between receptors.