P67-PHOX ENHANCES THE BINDING OF P47-PHOX TO THE HUMAN NEUTROPHIL RESPIRATORY BURST OXIDASE COMPLEX

The neutrophil respiratory burst oxidase consists of both the plasma membrane-associated flavocytochrome b(558) and cytosolic regulatory proteins including p47-phox, p67-phox, and a small GTP-binding protein (Rac1 and/or Rac2). Oxidase activation is thought to result from the assembly of the cytosolic components on the cytochrome. A model has been proposed in which p47-phox binds directly to the cytochrome, while p67-phox binding occurs indirectly by binding to p47-phox. We have carried out a steady state kinetic analysis using a cell free semirecombinant activation system (isolated plasma membrane plus recombinant cytosolic factors) to analyze the effects of p47-phox and p67-phox on one another's association in the active oxidase complex. As predicted from the model, increasing p47-phox concentration markedly lowered the EC(50) for p67-phox, indicating that p67-phox is dependent upon p47-phox for binding. Unexpectedly, increasing p67-phox concentration also produced a significant enhancement of p47-phox binding. Thus, a more complex binding model must be invoked in which p47-phox and p67-phox mutually enhance one another's binding.