Dinitrobenzenes Stimulate Electron Flux within Neuronal Nitric Oxide Synthase in the Absence of Calmodulin.

Efficient electron transfer and conversion of L-arginine to L-citrulline and nitric oxide (NO•) by neuronal nitric oxide synthase (nNOS) requires calmodulin (CaM) binding. The present study focused on electron transfer ability of resting state CaM-free nNOS in presence of dinitrobenzene isomers (DNBs). NADPH oxidation (NADPH ox ) and acetylated cytochrome-c reduction (AcCyt-cred ) catalyzed by nNOS and the CaM binding sequence-deficient nNOS reductase construct (nNOS-FP) were estimates of total electron flux and [Formula: see text] production, respectively. All the DNBs (o-, m-, p-) independently stimulated rates of NADPH ox by CaM-free nNOS and by nNOS-FP in isomer- and concentration-dependent manner. Blocking nNOS heme by imidazole or L-arginine did not affect CaM-free nNOS-catalyzed NADPH ox stimulated by DNBs. This stimulated electron flux by DNBs did not support NO• formation by CaM-free nNOS. The DNBs, like FeCN, extract electrons from both FMN and FAD of the nNOS reductase domain. All three DNBs greatly stimulated nNOS and nNOS-FP catalyzed AcCyt-cred that was significantly inhibited by SOD demonstrating [Formula: see text] formation. Thus, in presence of DNBs, resting-state CaM-deficient nNOS efficiently transfers electrons generating [Formula: see text], inferring that additional metabolic roles for nNOS exist that are not yet explored.