A search with Pertussis Toxin for Cellular Factors Affecting the Properties of GTP-Binding Protein

点击翻译按钮获取中文摘要

Pertussis toxin-catalyzed ADP-ribosylation of membrane Gi (inhibitory guanine nucleotide-binding protein) was examined on the hypothesis that the rate of modification may reflect the membrane environment of Gi. Incubation of saponin-permeabilized neutrophils with activated pertussis toxin and NAD led to rapid ADP-ribosylation of cellular Gi. The rate of ADP-ribosylation was found to be decreased by prior treatment of the cells with lipopolysaccharide (LPS), in spite that the cellular content of Gi was unaffected by the treatment. Receptor-mediated activation of Gi by formyl-peptide caused no change in the rate of the modification. LPS potentiated the formyl-peptide-induced activation of phospholipase C and increase in intracellular Ca^<++> in intact neutrophils. The changes were accompanied by the increased GDP-GTP exchange and GTP-hydrolyzing activities of Gi in membrane preparations. These results suggest that LPS-treatment of neutrophils causes Gi quantitative change or altered interaction with other cellular component, which affects the rate of pertussis toxin-catalyzed ADP-ribosylation.