C-60-fullerene monomalonate adducts selectively inactivate neuronal nitricoxide synthase by uncoupling the formation of reactive oxygen intermediates from nitric oxide production

C-60-Fullerene monomalonate adducts inactivate selectively the neuronal nit ric oxide synthase isoform in a manner completely preventable by the concur rent presence of superoxide dismutase and catalase. This inactivation is ti me-, fullerene concentration-, and turnover-dependent and is not reversible by dilution. The di(carboxypropan-3-ol)methano-[60]-fullerene (diol adduct ) has no effect on NADPH consumption by nNOS as measured in the absence of arginine substrate, but dramatically increases NADPH consumption in the pre sence of arginine. This fullerene-enhanced NADPH consumption is linked to o xygen as electron acceptor and is accompanied by the increased production o f hydrogen peroxide. These effects of fullerene monomalonate adducts an uni que to the nNOS isoform and are not observed using either the iNOS or the e NOS isoform. The inhibitory effects of fullerene monomalonate adducts are u naltered and insurmountable by increased concentrations of arginine, tetrah ydrobiopterin, or calmodulin. These observations indicate that fullerene mo nomalonate adducts uncouple in the presence of arginine the formation of re active oxygen intermediates from NO production by nNOS. These reactive oxyg en intermediates dissociate from the enzyme and, acting from solution, inac tivate NOS NO forming activity.