Electron spin resonance of O-labeled protein-peroxide radicals: Zein and edestin.

Hyperfine structure due to (17)O has been measured in irradiated zein and edestin after exposure to gaseous oxygen with (17)O concentrated to 24%. The observations prove that the free radicals produced by ionizing irradiation under vacuum at 300 K are converted by the oxygen to protein-peroxide free radicals X-O((1))-O((2)), with the unpaired electron density in a pi-type orbital predominantly on the peroxide group. From the observed couplings, the 2p(pi) spin densities on zein-peroxide are found to be 0.29 and 0.45 for O((1)) and O((2)), respectively; those on edestin-peroxide are 0.26 and 0.48 for O((1)) and O((2)), respectively.