title: A critical reevaluation of some assay methods for superoxide dismutase activity.
abstract: We have compared the direct method of pulse radiolysis to the indirect methods of cytochrome c and nitroblue tetrazolium for assaying the superoxide dismutase activity of a compound. We have shown that with pulse radiolysis, where high concentrations of O2- are generated, the "turnover" rate constant, kcat, can be determined directly, while with the indirect methods, where relatively low steady state concentrations of O2- are formed, the value of kcat determined by these methods, can be orders of magnitude lower than that determined directly. The main reason for the lower values obtained with the indirect methods is due to the fast reoxidation of the reduced compound by molecular oxygen. Additional problems which arise with the use of indirect methods for determining superoxide dismutase catalytic activity are discussed.
authors.affiliation: Department of Physical Chemistry, Hebrew University of Jerusalem, Israel.
authors.forename: S
authors.initials: S
authors.lastname: Goldstein
authors.forename: C
authors.initials: C
authors.lastname: Michel
authors.forename: W
authors.initials: W
authors.lastname: Bors
authors.forename: M
authors.initials: M
authors.lastname: Saran
authors.forename: G
authors.initials: G
authors.lastname: Czapski
mesh_terms: D003300:Copper; D003574:Cytochrome c Group; D004492:Edetic Acid; D006863:Hydrogen-Ion Concentration; D009580:Nitroblue Tetrazolium; D011675:Pulse Radiolysis; D013482:Superoxide Dismutase / Q000032:analysis* / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism
chemical_list: D003574:Cytochrome c Group; D013481:Superoxides; D009580:Nitroblue Tetrazolium; D003300:Copper; D004492:Edetic Acid; D013482:Superoxide Dismutase