A new route to peroxynitrite: a role for xanthine oxidoreductase

Peroxynitrite, a potent oxidising, nitrating and hydroxylating agent, resul ts from the reaction of nitric oxide with superoxide, We show that peroxyni trite can be produced by the action of a single enzyme, xanthine oxidoreduc tase (XOR), in the presence of inorganic nitrite, molecular oxygen and a re ducing agent, such as pterin. The effects of oxygen concentration on peroxy nitrite production have been examined. The physiologically predominant dehy drogenase form of the enzyme is more effective than the oxidase form under aerobic conditions. It is proposed that XOR-derived peroxynitrite fulfils a bactericidal role in milk and in the digestive tract. (C) 2000 Federation of European Biochemical Societies. Published by Elsevier Science B.V. All r ights reserved.