The aim of the project is to investigate the reaction mechanism of the important enzyme neuronal Nitric Oxide Synthase(nNOS). nNOS catalyses the oxidation of 1-arginine by molecular oxygen to citrulline and the important signalling molecule NO. The reacti on cycle is proposed to include many intermediates, among others the protonated radical trihydrobiopterine and reactive oxygen species. Trapping and characterization of these intermediates will help us elucidate the reaction mechanism. Cloning and overexp ression of site-directed mutants will help trapping intermediates in the catalytic cycle of nNOS.