3-Nitropropionate (3-NPA) is a toxin that is produced by various organisms as a protection mechanism against predators. This toxin naturally occurs as an ester glycoside and can be hydrolyzed by the intestinal flora after ingestion. Once hydrolyzed, the toxin can be fatal by halting the Krebs cycle and the electron transport chain. Nitronate monooxygenase from Neurospora crassa(NcNMO), an FMN-dependent enzyme, catalyzes the oxidation of 3-NPA via a single electron transfer. In this study, we investigated the kinetic mechanism of NcNMO using steady-state and rapid kinetics with 3-NPA as substrate in the presence of various concentrations of viscosigen. The rate of the reductive half-reaction, which is not diffusion-controlled, increased with added viscosigen suggesting that the electron transfer is gated by a slower conformational change.