ROLE OF GDP IN FORMYL-PEPTIDE-RECEPTOR-INDUCED ACTIVATION OF GUANINE-NUCLEOTIDE-BINDING PROTEINS IN MEMBRANES OF HL-60 CELLS

Membranes of myeloid differentiated human leukemia (HL 60) cells contain receptors for the chemotactic peptide, fMet-Leu-Phe (fMet, N-formylmethionine), interacting with pertussis-toxin-sensitive guanine-nucleotide-binding proteins (G proteins). Agonist activation of the receptors increases binding of the GTP analog, guanosine 5'-[gamma-thio]triphosphate (GTP[S]), to membrane G proteins, at 30-degrees-C only in the presence of exogenous GDP. In contrast, at O-degrees-C fMet-Leu-Phe stimulated binding of GTP[S] to G proteins maximally without addition of GDP. Under conditions resulting in marked degradation of membrane-bound GDP, control binding of GTP[S] measured at O-degrees-C was significantly increased, whereas the extent of agonist-stimulated binding was reduced. Furthermore, there was a rapid spontaneous release of membrane-bound GDP at 30-degrees-C, but not at O-degrees-C. The data suggest that in intact membranes of HL 60 cells G proteins are initially in a GDP-liganded form, which state allows the receptor-induced exchange of bound GDP for GTP[S] at low temperature. In contrast, at or near physiological temperature, bound GDP is rapidly released (and degraded), resulting in unligated G proteins to which GTP[S] will bind independently of agonist-activated receptors.