Does copper (II) ethylenediaminetetraacetate disproportionate superoxide?

W. M. Willingham and J. R. J. Sorenson have recently reported [1988) Biochem. Biophys. Res. Commun. 150, 252-258) that the Cu(II)EDTA complex catalyzes the dismutation of O-2 and thereby call into question several earlier reports. These authors concluded that the widespread use of EDTA to suppress dismutation of O-2 by adventitious Cu(II) and other metals, during assays for superoxide dismutase, is unsound. We have undertaken a clarification of this issue by examining the ability of Cu(II)EDTA to catalyze the dismutation of O-2 and have found this complex to be devoid of this activity at pH 6.0 or at 7.8; whether assayed by the cytochrome c or the nitroblue tetrazolium assays. The probable reasons for the results of Willingham and Sorenson and some peculiarities of the nitroblue tetrazolium assay have been explored.