A Paramagnetic Oxygen Intermediate

On adding dioxygen to the fully reduced laccase of the lacquer tree Rhus vemicifera, the type-1 Cu and the type-3 Cu-pair were oxidized in the ms range and an optical intermediate was observed at 360 nm At liquid helium temperatures an EPR signal was observed, which was tentatively interpreted as due to O , as a result of its very short relaxation time and of the increase of its linewidth when the reduced laccase of the fungus Polyporus versicolor was treated with 0 A similar paramagnetic oxygen intermediate was also observed with the laccase of another lacquer tree Rhus succedanea and with ceruloplasmin. The decay of the intermediate at 25 °C (tj = 1 s at pH 5.5 with R. succedanea laccase) was accompanied by the reoxidation of the type-2 Cu . One would expect, however, such an intermediate to be extremely reactive (See Sect. 3.3), while it was stable in tree laccase depleted of type-2 Cu(II) 

A new broad EPR resonance at g = 5 was observed by rapid freezing on treating reduced cytochrome c oxidase with Oj. It could not be attributed to an oxygen containing radical, as the linewidth was not increased with O  

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