On the mechanism of inhibition of the neutrophil respiratory burst oxidase by a peptide from the C-terminus of the large subunit of cytochrome b558.

A peptide (RGVHFIF) from near the carboxyl terminus (residues 559-565) of gp91-phox, the large subunit of cytochrome b558, was previously shown to inhibit activation of the respiratory burst oxidase [Kleinberg, M. E., Malech, H. L., & Rotrosen, D. (1990) J. Biol. Chem. 265, 15577-15583]. The peptide has been proposed to compete with gp91-phox binding to p47-phox, one of the cytosolic oxidase components. In the present studies, we have used a semirecombinant system consisting of recombinant cytosolic factors (p47-phox, p67-phox, and Rac1) along with isolated plasma membrane to investigate the mechanism by which the peptide inhibits oxidase activation. In an in vitro translocation model, the peptide inhibited arachidonate-activated translocation of both p47-phox and p67-phox to the plasma membrane. The kinetic mechanism of inhibition was examined. Inhibition was noncompetitive or mixed with respect to not only Rac and p67-phox but also to p47-phox. We suggest that the peptide, rather than competing for cytochrome-p47-phox interactions, inhibits indirectly, perhaps by binding to and altering the conformation of cytochrome b558.