On the geometry of leukocyte NADPH‐oxidase, a membrane flavoenzyme

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Abstract
Using the structure of glutathione reductase as a model, we suggest the following topography for leukocyte NADPH‐oxidase: The binding sites of NADPH and O2 are separated from each other by the flavin ring and are thus exposed to opposite sides of the plasma membrane. This model supports the concept that O− 2 is formed at the membrane facing the extracellular or phagosomal space, respectively. The fate of the proton produced in the reaction NADPH + 2 O2 → NADP + 2 O− 2 + H+ is also discussed in light of our model. NAD(P)H‐oxidases possessing the topography of glutathione reductase may establish transmembrane proton gradients. Consequently our model suggests that leukocyte NADPH‐oxidase produces not only the O− 2 burst but also a proton burst.