Figure 9. Schematic representation of the involvement of a membrane localized NDPK in NADPH oxidase activation. The scheme proposes the existence of a linkage between GEF-induced dissociation of GDP from RacGDP and γ-phosphoryl transfer from ATP to free GDP, by NDPK, resulting in the formation of GTP, which is then bound to Rac, to generate RacGTP. It is also suggested that 3 components participating in GDP dissociation and GDP phosphorylation (prenylated Rac, GEF, and NDPK) are attached to the membrane and are, possibly, co-localized in micro-domains. A hypothetical integration of GEF and NDPK with the subunits of the NADPH oxidase complex is also proposed (modified from ref. 130).