Nitric oxide is synthesized in mammalian cells from L-arginine or from
pharmaceutical drugs. It forms paramagnetic complexes with some metal
loproteins, inhibiting key enzymes in DNA synthesis, mitochondrial res
piration, iron metabolism, etc. This article reviews how electron para
magnetic resonance spectroscopy helps to detect unambiguously such spe
cific molecular targets for NO in mammalian whole cells and organelles
. EPR has also been used for the detection of spin adducts of free NO
by spin-trapping methods.