GTP-dependent and -independent activation of superoxide producing NADPH oxidase in a neutrophil cell-free system.

GTP and GTP-gamma-S enhanced several-fold the NADPH-dependent superoxide production induced by sodium dodecyl sulfate in a cell-free system of pig neutrophils consisting of the membrane fraction and two cytosolic fractions separated by gel filtration. The enhanced activity was decreased by the addition of GDP in a dose-dependent manner, but 70% of the activity in the absence of GTP remained even at 1 mM GDP. Only one cytosol fraction besides the membrane fraction was required for the activation in the presence of GTP. The cytosol fraction was analyzed by chromatography on 2',5'-ADP agarose and two components responsible for the GTP-dependent and independent activation were separated. These results suggest that at least two pathways are available for the activation of superoxide production in the cell-free system of pig neutrophils.