ABSTRACT
NADPH oxidase is a large enzyme complex in the phagosome membrane that is assembled from component parts in the membrane and the cytosol in response to a phagocytic stimulus. Not all of the components of this multisubunit complex have been defined clearly but at least two, p47phox and p67phox, reside in the cytoplasm in unstimulated phagocytes, whereas two others together comprise the membrane complex cytochrome b558. The two chains of cytochrome b558 are a heavy chain, gp91phox, and a light chain, p21phox, which contains the catalytic site (Fig. 2.3). The genes encoding p47phox, p67phox, and p21phox map to autosomal chromosomes, whereas gp91phox is encoded on the short arm of the X chromosome. Four different genetic defects affect various components of the NADPH oxidase enzyme but they all result in a disease with a common phenotype, called chronic granulomatous disease (CGD). The commonest form of the disease is X-linked CGD, which is caused by mutations in the gene encoding gp91phox.
