The phagocyte NADPH oxidase, dormant in resting cells, is activated during phagocytosis to produce superoxide, a precursor of microbicidal oxidants. The activated oxidase is a complex of membrane-integrated cytochrome bs58, composed of 91-kDa (gp91PbOx) and 22-kDa (p22PIox) subunits, and two cytosolic factors (p47PbOX and p67Pb°'), each containing two Src homology 3 (SH3) domains.Here we show that the region of the tandem SH3 domains of p47Phox (p47-SH3) expressed as a glutathione S-transferase fusion protein inhibits the superoxide production in a cell-free system, indicating involvement of the domains in the activation. Furthermore, we find that arachidonic acid and sodium dodecyl sulfate, activators of the oxidase in vitro, cause exposure of p47-SH3, which has probably been masked by the C-terminal region of this protein in a resting state. The unmasking of p47-SH3 appears to play a crucial role in the assembly of the oxidase components, because p47-SH3 binds to both p22PhO and p67PhOx but fails to interact with a mutant p22Phox carrying a Pro-156 -* Gln substitution in a prolinerich region, which has been found in a patient with chronic granulomatous disease. Based on the observations, we propose a signal-transducing mechanism whereby normally inaccessible SH3 domains become exposed upon activation to interact with their target proteins.During ingestion of microbes or upon stimulation with various soluble molecules, neutrophils and other phagocytic cells produce superoxide (O°), a precursor of microbicidal oxidants (1-4). The process involves activation ofthe phagocyte NADPH oxidase, dormant in resting cells, that catalyzes reduction of molecular oxygen to superoxide in conjunction with oxidation of NADPH. The significance of the NADPH oxidase in host defense is made evident by recurrent and life-threatening infections that occur in patients with chronic granulomatous disease (CGD) whose phagocytes lack the superoxide-producing system (1-4).The active NADPH oxidase is found on the phagocyte membrane as an enzyme complex, the components ofwhich are identified as targets of genetic defects causing CGD. The one identified at an earlier stage is a phagocyte-specific membrane-integrated b-type cytochrome, cytochrome b558 (5-11), composed of 91-kDa and 22-kDa subunits (designated gp91Phox and p22PhOX, respectively). The cytochrome is now considered to be a flavocytochrome comprising an apparatus transporting electrons from NADPH via FAD and then heme to molecular oxygen (12)(13)(14)(15)(16) . In addition to these specialized factors, as a third cytosolic factor, the small GTPbinding protein p21rac (rac 1 and/or rac 2) is also involved in the system (22)(23)(24).Although the components of the NADPH oxidase are thus identified, little is known about the mechanism for their assembly leading to activation of the enzyme. Upon phagocyte stimulation, the cytosolic components translocate to the membrane where cytochrome b558 resides (25,26). Experiments using neutrophils from CGD patients have revealed that the t...

No abstract

1. Both NADH and NADPH supported the oxidation of adrenaline to adrenochrome in bovine heart submitochondrial particles. The reaction was completely inhibited in the presence of superoxide dismutase, suggesting that superoxide anions (O(2) (-)) are responsible for the oxidation. The optimal pH of the reaction with NADPH was at pH7.5, whereas that with NADH was at pH9.0. The reaction was inhibited by treatment of the preparation with p-hydroxymercuribenzoate and stimulated by treatment with rotenone. Antimycin A and cyanide stimulated the reaction to the same extent as rotenone. The NADPH-dependent reaction was inhibited by inorganic salts at high concentrations, whereas the NADH-dependent reaction was stimulated. 2. Production of O(2) (-) by NADH-ubiquinone reductase preparation (Complex I) with NADH or NADPH as an electron donor was assayed by measuring the formation of adrenochrome or the reduction of acetylated cytochrome c which does not react with the respiratory-chain components. p-Hydroxymercuribenzoate inhibited the reaction and rotenone stimulated the reaction. The effects of pH and inorganic salts at high concentrations on the NADH- and NADPH-dependent reactions of Complex I were essentially similar to those on the reactions of submitochondrial particles. 3. These findings suggest that a region between a mercurialsensitive site and the rotenone-sensitive site of the respiratory-chain NADH dehydrogenase is largely responsible for the NADH- and NADPH-dependent O(2) (-) production by the mitochondrial inner membranes.

The thioredoxin/thioredoxin reductase system has been studied as regenerative machinery for proteins inactivated by oxidative stress in vitro and in cultured endothelial cells. Mammalian glyceraldehyde-3-phospliate dehydrogenase was used as the main model enzyme for monitoring the oxidative damage and the regeneration. Thioredoxin and its reductase purified from bovine liver were used as the regenerating system. The physiological concentrations (2 -14 pM) of reduced thioredoxin, with 0.125 pM thioredoxin reductase and 0.25 mM NADPH, regenerated H202-inactivated glyceraldehyde-3-phosphate dehydrogenase and other mammalian enzymes almost completely within 20 min at 37°C. Although the treatment of endothelial cells with 0.2-12 mM H 2 0 2 for 5 min resulted in a marked decrease in the activity of glyceraldehyde-3-phosphate dehydrogenase, it had no effect on the activities of thioredoxin and thioredoxin reductase. Essentially all of the thioredoxin in endothelial cells at control state was in the reduced form and 70-85% remained in the reduced form even after the H 2 0 2 treatment. The inactivated glyceraldehyde-3-phosphate dehydrogenase in a cell lysate prepared from the H,02-treated endothelial cells was regenerated by incubating the lysate with 3 mM NADPH at 37 "C and the antiserum raised against bovine liver thioredoxin inhibited the regeneration. The inhibition of thioredoxin reductase activity by 13-cis-retinoic acid resulted in a decrease in the regeneration of glyceraldehyde-3-phosphate dehydrogenase in the H202-treated endothelial cells. The present findings provide evidence that thioredoxin is involved in the regeneration of proteins inactivated by oxidative stress in endothelial cells.

No abstract