Structural and functional analogs of CuZn superoxide dismutase inhibit rat brain nitric oxide synthase by interference with the reductase (diaphorase) domain.

Copper complexes with superoxide dismutase (SOD) activity show a wide range of pharmacological activities. We have investigated the effect of ([N,N'-bis(2-pyridylmethylene)-1,4-butanediamine]-(N,N',N", N"')]-Cu(II)-chloride (Cu-PuPy) and ([N,N'-bis(2-pyridyl-phenyl)methylene-1,4-butanediamine]-(N,N',N", N"'))-Cu(II)-chloride (Cu-PuPhePy) on the multiple catalytic functions of rat brain NO synthase (NOS). Both drugs inhibited the formation of L-citrulline as well as the enzymatic reduction of cytochrome c. The uncoupled oxidation of NADPH, catalyzed by neuronal NOS in the absence of L-arginine, was inhibited by Cu-PuPy but stimulated by Cu-PuPhePy, suggesting that the phenyl-substituted compound acts as a parasitic electron acceptor. Our data identify copper complexes with SOD mimicking activity as a novel class of neuronal NOS inhibitors blocking the reductase (diaphorase) activity of the enzyme.