A novel procedure for generating both nitric oxide and superoxide in situ from chemical sources at any chosen mole ratio. First application: tyrosine oxidation and a comparison with preformed peroxynitrite.

The first method for generating (*)NO and O(2)(*)(-) at any known, constant ratio has been developed. Spermine NONOate and di(4-carboxybenzyl)hyponitrite decay with first-order kinetics and exactly equal rate constants (half-lives of 80 min) at 37 degrees C and pH 7.5 to give 200 and 40 mol % (*)NO and O(2)(*)(-), respectively. Tyrosine oxidation to dityrosine and 3-nitrotyrosine (the major and minor products under the conditions used in these experiments) has been studied (mainly in the presence of CO(2)) using various different ratios of the rates of formation of (*)NO and O(2)(*)(-). The (*)NO/O(2)(*)(-) = 1.0 product profiles are very similar to those of the products derived from equal amounts of (*)NO and O(2)(*)(-) generated at a (*)NO/O(2)(*)(-) ratio of 1.0 from SIN-1 but are very different from those derived from preformed peroxynitrite. All the experimental results can be explained in terms of free radical chemistry. The product profiles at all the (*)NO/O(2)(*)(-) ratios could be satisfactorily simulated provided an important group of reactions which lead to the consumption of dityrosine was included.