Nature and functioning of the pertussis toxin-sensitive G protein of neutrophils

A specific, pertussis toxin-sensitive, GTP binding, regulatory protein of neutrophils which we term "Gn" couples the reaction of chemotactic factors with their specific receptors to the resultant stimulation of chemotaxis, granule enzyme secretion, O2- generation, aggregation etc. The ability of four chemotactic formylpeptides to increase the GTPase activity of isolated plasma membranes of rabbit neutrophils correlates almost perfectly with the ability of the same peptides to cause granule enzyme release. These and other findings provide formal evidence for the previous assumption that fMET-Leu-Phe increases the GTPase activity of Gn by reacting with the same receptor that triggers granule enzyme release and other stimulated functions of the neutrophil. The molecular weight of 40 kDa and isoelectric point of 5.5 of the [32P] ADP-ribosylated alpha subunit of Gn, differ slightly but significantly from the corresponding alpha subunits of the other G proteins that are substrates for pertussis toxin. Differences also exist in the patterns of proteolytic fragments of the alpha subunit of Gn and those of the other G proteins. These observations indicate that in neutrophils a G protein distinct from the previously identified pertussis toxin substrates couples the stimulation of chemotactic receptors to the physiological function of cells. The dissociation constants of binding (Kd) for the high and low affinity sites of the formylpeptide receptor of rabbit peritoneal neutrophils and the ability to induce secretion of beta glucosaminidase from the same cells were determined for each of seven chemotactic formylpeptides.(ABSTRACT TRUNCATED AT 250 WORDS)