A chemoattractant receptor on macrophages exists in two affinity states regulated by guanine nucleotides

The binding characteristics of the oligopeptide chemoattractant receptor on guinea pig macrophages and macrophage membrane preparations were characterized using detailed binding studies and computer analysis. Viable macrophages bound the radiolabeled chemoattractant N- formyl-methionyl-leucyl-[3H]phenylalanine with single dissociation constant (KD) of 18.4 +/- 4.6 nM with 15,300 +/- 1,800 sites per cell. Binding data from membrane preparations indicated the presence of two classes of binding sites with KD of 1.5 +/- 0.4 nM and 25.5 +/- 11.0 nM. Approximately 23% of the receptors were in the high affinity state. In the presence of added guanine nucleotide di- or triphosphates, the high affinity receptors in the membrane preparations were converted to low affinity states with no change in the total receptor number. Nonhydrolyzable derivatives of GTP were most potent in converting the receptor from its high to low affinity state. These data suggest that the affinity state of the oligopeptide chemoattractant receptor in macrophages is regulated by guanine nucleotides and GTPase, implying that the transduction mechanisms of this receptor may be controlled by a guanine nucleotide regulatory unit.