Can nitric oxide be spin trapped by nitrone and nitroso compounds?

Increasing interest in the study of nitric oxide (NO.) in many facets of biological research necessitates a search for accurate techniques to directly identify the free radical. One recently employed strategy for NO. detection is the method of electron spin resonance (ESR) used in combination with nitrone and nitroso spin traps. Applying this technique to our studies with nitric oxide synthase (NOS), we found that NO. generated directly from the enzyme system could not be detected. Further investigation revealed that 3,5-dibromo-4-nitrosobenzenesulfonic acid (DBNBS) inhibited NO. generation by NOS at concentrations used for spin trapping. Reexamining the ability of various nitrones and DBNBS to spin trap authentic NO. dissolved in buffer, we obtained ESR spectra similar to those previously reported for the spin trap DBNBS. However, continuing our studies with 15NO. and N-hydroxylamine, we found these spectra to be artifactual. Our results emphasize the need to synthesize new spin traps, since currently available compounds are not capable of spin trapping NO. generated by NOS.