The discovery of mammalian nitric oxide (NO-) synthesis from I-ar- ginine has led to profound increases in our understanding of basic physiological and pathophysiological processes. This understanding has been achieved by major advances in several areas. Three major ni- tric oxide synthase (NOS) isoforms have been identified at the protein and gene level and their specific tissue localization has been linked to processes subject to regulation by NO-. The molecular basis for the di- verse effects of NO- on cell function has been shown to derive from its chemical reactivity with...