Electron spin resonance of nitric oxide- hemoglobin complexes in solution.

The electron spin resonance spectra of solutions of nitric oxide-hemoglobin and nitric oxide-methemoglobin, and whole blood treated at room temperature with nitric oxide, all exhibit resonance with a line width of 83 gauss, a g-value of 2.03, and a spin intensity corresponding to one unpaired electron spin per heme. The minimum detectable concentration of these nitric oxide complexes in solution is 10(-5)M. Solutions were stable in a nitrogen atmosphere but when exposed to air in the absence of nitric oxide the spin intensity decreased with a half-life of about 5 hours. A preliminary examination of blood of rats exposed 1 and 9 days to 10 ppm of nitric oxide in air showed no electron spin resonance.