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 (Met, N ‐formylmethionine), interacting with pertussis‐toxin‐sensitive guanine‐nucleotide‐binding proteins (G proteins). Agonist activation of the receptors in‐ creases binding of the GTP analog, guanosine 5′‐[γ‐thioltriphosphate (GTP[S]), to membrane G proteins, at 30°C only in the presence of exogenous GDP. In contrast, at 0°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 0°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°C, but not at 0°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.