Peroxynitrite: reactive, invasive and enigmatic.

The reactive oxygen and nitrogen species superoxide ion, nitric oxide, nitrogen dioxide and peroxynitrite ion all react with biological target molecules. Some of these interactions are carefully orchestrated segments of signal transduction cascades or part of the armamentarium of the immune system, others are pathological events and may lie at the root of many diseases. As a result of these small reactive molecules, proteins, particularly metalloproteins, can be altered with loss of function, DNA can be cleaved and lipid components can be oxidized to disrupt membranes. The interactions of these species with each other and their aftermath can be sensed by the cell, resulting in a variety of responses including gene regulation and transcription. Indeed, there is recent, tantalizing evidence that the currency of reactive oxygen and nitrogen species is central to the life and death cellular decisions in homeostasis or the initiation of apoptosis. New families of metallopharmaceuticals may serve both to probe the nature and mechanisms of these events and to effect the outcome.