Inducible NO synthase: Role in cellular signalling

The discovery of endothelium-derived relaxing factor and its identification as nitric oxide (NO) was one of the most exciting discoveries of biomedica l research in the 1980s. Besides its potent vasodilatory effects, NO was fo und under certain circumstances to be responsible for the killing of microo rganisms and tumour cells by activated macrophages and to act as a novel, u nconventional type of neurotransmitter. In 1992, Science picked NO as the ' Molecule of the Year', and over the past years NO has become established as a universal intercellular messenger that acutely affects important signall ing pathways and, on a more long-term scale, modulates gene expression in t arget cells. These actions will form the focus of the present review.