Potential roles of Mg2+ and Ca2+ in NADPH oxidase dependent superoxide anion synthesis by human neutrophils.
Recent studies have shown that, in cell free systems, Mg2+, but not Ca2+, is absolutely required for the generation of reducing equivalents by neutrophil NADPH oxidase. Apparently Mg2+ is required for binding of cytosolic protein(s) to the plasma membrane in forming a functional NADPH oxidase complex. Using intact neutrophils made permeable to Mg2+ and Ca2+ by A23187 it was found that Mg2+ was required for the generation of reducing equivalents by PMA stimulated cells while Ca2+ inhibited cytochrome c reduction. On the other hand, FMLP-induced neutrophils were unable to generate reducing equivalents unless both Ca2+ and Mg2+ were present in the media. Sequential addition of these cations indicated that Ca2+ was required for transduction of the FMLP-receptor generated signal to a point in the pathway where Mg2(+)-dependent synthesis of reducing equivalents occurred. This step, presumably, is the Mg2(+)-dependent completion of the NADPH oxidase complex. Finally, approximately 50% of the neutrophil's 2.19 fmoles (6.32 mM) of Mg2+ was found to be in a readily exchangeable pool and that pretreatment of neutrophils with either FMLP or PMA increased this pool by only 4-5%. This suggests there is an adequate pool of Mg2+ available to support completion of NADPH oxidase complex and that a stimulus-induced rise in free Mg2+ is not required to assist in the formation of the complex.
Gabler
W L
WL
Department of Biochemistry, School of Dentistry, Oregon Health Sciences University, Portland.
D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology*; D002478:Cells, Cultured; D006801:Humans; D008274:Magnesium / Q000032:analysis / Q000378:metabolism / Q000494:pharmacology*; D009113:Muramidase / Q000378:metabolism; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009247:NADH, NADPH Oxidoreductases / Q000502:physiology*; D019255:NADPH Oxidases; D009504:Neutrophils / Q000378:metabolism*; D013481:Superoxides / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
D013481:Superoxides; D000001:Calcimycin; D009240:N-Formylmethionine Leucyl-Phenylalanine; D009247:NADH, NADPH Oxidoreductases; D019255:NADPH Oxidases; D009113:Muramidase; D008274:Magnesium; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium