Binding characteristics of receptors for phagocytosis on the surface of Amoeba proteus

Binding of the tripeptide n-formylmethionyl-leucylphenylalanine (NFMLP) to phagocytic receptors on the surface of Amoeba proteus was examined. Peptide-binding is reversible and demonstrates saturation kinetics. The receptors for phagocytosis are internalized by a temperature-sensitive process with indications that the receptors are recycled. The amoeba is capable of down-regulating its receptors for phagocytosis in response to constant external peptide levels, and also increasing the number of surface receptors in response to food deprivation. On the basis of competition studies, there is evidence that Amoeba proteus has separate surface receptors for both pinocytosis and phagocytosis.