title: Purification and characterization of a membrane-bound NADPH-cytochrome c reductase capable of catalyzing menadione-dependent O2- formation in guinea pig polymorphonuclear leukocytes.
abstract: A membrane-bound NADPH-cytochrome c reductase, which is capable of forming the superoxide anion (O2-) in the presence of menadione, was highly purified from membrane fractions of disrupted guinea pig polymorphonuclear leukocytes by solubilization with 0.2% Triton X-100 and chromatographies on Sephacryl S-300 and 2',5'-ADP-agarose. The overall purification from the membrane fraction was over 110-fold, with a yield of about 6%. The purified preparation did not contain two other pyridine nucleotide-oxidizing enzymes: NADH- and NAD(P)H-oxidizing enzymes (J. Biochem. 94, 931-936, 1983). Besides cytochrome c, the purified enzyme was able to reduce menadione, Nitroblue tetrazolium (NBT) and 2,6-dichlorophenolindophenol. The reduction of menadione alone resulted in the formation of O2-. The purified enzyme preparation contained FAD. When assayed by measuring O2--generation in the presence of menadione, the enzyme showed an optimum pH at 7.0-7.4, and Km values for NADPH, NADH, and menadione were 25, 230, and 5.3 microM, respectively. The enzyme activity was not inhibited by NaN3 or dicumarol, but was by N-ethylmaleimide, EDTA, and quercetin; these inhibition profiles agree with those observed for the NADPH oxidase in the membrane fraction of phorbol-myristate acetate-stimulated leukocytes. Furthermore, when compared by means of the NBT-staining method combined with disc gel electrophoresis, the purified enzyme was electrophoretically indistinguishable from the NADPH-NBT reductase in the plasma membrane as well as phagosomes of the leukocytes. These results suggest that the purified NADPH-cytochrome c reductase is the putative flavoprotein of the NADPH oxidase system responsible for the respiratory burst.
mesh_terms: D000818:Animals; D002462:Cell Membrane / Q000201:enzymology; D005486:Flavin Mononucleotide / Q000032:analysis; D005182:Flavin-Adenine Dinucleotide / Q000032:analysis; D006168:Guinea Pigs; D007700:Kinetics; D009251:NADPH-Ferrihemoprotein Reductase / Q000097:blood* / Q000302:isolation & purification; D009504:Neutrophils / Q000187:drug effects / Q000201:enzymology*; D013481:Superoxides / Q000097:blood*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014812:Vitamin K / Q000494:pharmacology*
chemical_list: D013481:Superoxides; D014812:Vitamin K; D005182:Flavin-Adenine Dinucleotide; D005486:Flavin Mononucleotide; D009251:NADPH-Ferrihemoprotein Reductase; D013755:Tetradecanoylphorbol Acetate