ON THE MECHANISM OF INHIBITION OF THE NEUTROPHIL RESPIRATORY BURST OXIDASE BY A PEPTIDE FROM THE C-TERMINUS OF THE LARGE SUBUNIT OF CYTOCHROME B(558)

A peptide (RGVHFIF) from near the carboxyl terminus (residues 559-565) of gp91-phox, the large subunit of cytochrome b(558), was previously shown to inhibit activation of the respiratory burst oxidase [Kleinber g, M. E., Malech, H. L., and Rotrosen, D. (1990) J. Biol. Chem. 265, 1 5577-15583]. The peptide has been proposed to compete with gp91-phox b inding to p47-phox, one of the cytosolic oxidase components. In the pr esent studies, we have used a semirecombinant system consisting of rec ombinant cytosolic factors (p47-phox, p67-phox, and Rac1) along with i solated plasma membrane to investigate the mechanism by which the pept ide inhibits oxidase activation. In an in vitro translocation model, t he peptide inhibited arachidonate-activated translocation of both p47- phox and p67-phox to the plasma membrane. The kinetic mechanism of inh ibition was examined. Inhibition was noncompetitive or mixed with resp ect to not only Rac and p67-phox but also to p47-phox. We suggest that the peptide, rather than competing for cytochrome-p47-phox interactio ns, inhibits indirectly, perhaps by binding to and altering the confor mation of cytochrome b(558).