NITRIC-OXIDE INACTIVATES NADPH OXIDASE IN PIG NEUTROPHILS BY INHIBITING ITS ASSEMBLING PROCESS

The effects of nitric oxide (NO) on superoxide (O-2 radical anion) gen eration of the NADPH oxidase in pig neutrophils were studied, NO dose- dependently suppressed O-2 radical anion generation of both neutrophil NADPH oxidase and reconstituted NADPH oxidase. Effects of NO on NADPH -binding site and the redox centers including FAD and low spin heme in cytochrome b(558) and the electron transfer rates from NADPH to heme via FAD were examined under anaerobic 'conditions. Both reaction rates and the K-m value for NADPH were unchanged by NO. Visible and EPR spe ctra of cytochrome b(558) showed that the structure of heme was unchan ged by NO, indicating that NO does not affect the redox centers of the oxidase. In reconstituted NADPH oxidase system, NO did not inhibit O- 2 radical anion generation of the oxidase when added after activation. The addition of NO to the membrane component or the cytosol component inhibited the activity by 24.0 +/- 5.3 or 37.4 +/- 7.1%, respectively . The addition of NO during the activation process or to the cytosol c omponent simultaneously with myristate inhibited the activity by 74.0 +/- 5.2 or 70.0 +/- 8.3%, respectively, suggesting that cytosol protei n(s) treated with myristate becomes susceptible to NO, Peroxynitrite d id not interfere with O-2 radical anion generation.