Involvement of GTP in cell-free activation of neutrophil NADPH oxidase. Studies with GTP analogues

Activation of superoxide-producing NADPH oxidase of neutrophils requires the presence of cell membranes, cytosolic components and arachidonate and is markedly enhanced by non-hydrolysable analogues of guanine nucleotides, i.e. guanosine 5'-[γ-thio]triphosphate and guanosine 5'-[βγ-imido]triphosphate (p[NH]ppG]. Gel filtration and ultrafiltration of the cytosol decreased the basal activity of NADPH oxidase. Activity could be restored by GTP, suggesting participation of the nucleotide in basa] activation. Preincubation of neutrophil cytosol with periodate-oxidized p[NH]ppG (ox-p[NH]ppG) followed by gel filtration resulted in a time-dependent enhancement of basa] oxidase activity. The presence of GDP or GTP, but not ATP, during the incubation with ox-p[NH]ppG abolished this enhancement. These data are consistent with a stable association of ox-p[NH]ppG with an oxidase-linked cytosolic protein SDS/PAGE of neutrophil cytosol preincubated with [³H]ox-p[NH]ppG revealed radioactivity in bands migrating as 100, 70, 47, 34 and 22 kDa proteins. Evidence for covalent labelling of the cytosolic protein p47-phox with [³H]ox-p[NH]ppG is presented. Heterogencity of cytosolic GTP-binding sites and possible participation of protein p47-phox in functional interaction with GTP analogues during cell-free activation are suggested.