Abstract
The superoxide (O-2)-generating NADPH oxidase of phagocytes is a multicomponent complex consisting of a membrane-associated flavocytochrome (cytochrome b559), bearing the NADPH binding site and two redox centers (FAD and heme) and three cytosolic activating components: p47(phox), p67(phox), and the small GTPase Rac (1 or 2). The canonical view is that the induction of O-2 generation involves the stimulus-dependent assembly of all three cytosolic components with cytochrome b559, a process mimicked in vitro by a cell-free system activated by anionic amphiphiles. We studied the requirement for individual cytosolic components in the activation of NADPH oxidase in a cell-free system consisting of purified and relipidated cytochrome b559, recombinant p47(phox), p67(phox), and Rac1, and the amphiphile, lithium dodecyl sulfate. We found that pronounced activation of NADPH oxidase can be achieved by exposing cytochrome b559 to p67(phox) and Rac1, in the total absence of p47(phox) (turnover = 60 mol O-2/s/mol cytochrome b559). However, maximal activation (turnover = 153 mol O-2/s/mol cytochrome b559) could only be obtained in the presence of p47(phox). O-2 production, in the absence of p47(phox), was dependent on: high molar ratios of p67(phox) and Rac1 to cytochrome b559, Rac1 being in the GTP-bound form, cytochrome b559 being saturated with FAD, and an optimal concentration of amphiphile. Single cytosolic components or combinations of two cytosolic components, other than p67(phox) and Rac1, were incapable of activation. We conclude that p67(phox) and Rac1 are the only cytosolic components directly involved in the induction of electron transport in cytochrome b559. p47(phox) appears to facilitate or stabilize the interaction of p67(phox) and, possibly, Rac1 with cytochrome b559, and is required for optimal generation of O-2 under physiological conditions.
Highlights
NADPH oxidase in a cell-free system consisting of purified and relipidated cytochrome b559, recombinant p47phox, p67phox, and Rac1, and the amphiphile, lithium dodecyl sulfate
The activation of NADPH oxidase can be mimicked in vitro by a cell-free system consisting, in its most basic form, of membranes and the cytosolic fraction of resting phagocytes exposed to a critical concentration of some anionic amphiphiles (12–16)
Cross et al (24) demonstrated that the activated NADPH oxidase possessed a diaphorase activity, which was dependent on p67phox but not on p47phox. They went on to show that the two cytosolic components have unequal roles in the regulation of electron flow in cytochrome b559; p67phox stimulated the flow from NADPH to FAD, whereas p47phox was required for electron transport from FAD to heme and oxygen (25)
Summary
NADPH oxidase in a cell-free system consisting of purified and relipidated cytochrome b559, recombinant p47phox, p67phox, and Rac1, and the amphiphile, lithium dodecyl sulfate. The activation of NADPH oxidase can be mimicked in vitro by a cell-free system consisting, in its most basic form, of membranes and the cytosolic fraction of resting phagocytes exposed to a critical concentration of some anionic amphiphiles (12–16).
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