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Decay of the HO 2 and O − 2 Radicals Catalyzed by Superoxide Dismutase. A Pulse Radiolytic Investigation
Author(s) -
Rabani Joseph,
Klug Dina,
Fridovich Irwin
Publication year - 1972
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.197200117
Subject(s) - chemistry , radiolysis , radical , superoxide , superoxide dismutase , formate , sodium formate , reaction rate constant , aqueous solution , photochemistry , inorganic chemistry , nuclear chemistry , catalysis , enzyme , kinetics , organic chemistry , physics , quantum mechanics
The pulse radiolysis technique has been employed in the investigation of the dismutation of superoxide radicals, O − 2 and HO 2 , in the presence of superoxide dismutase in aqueous solutions. The decay of superoxide radicals in the presence of the enzyme was found to be first order in both enzyme and superoxide concentrations. An apparent second order reaction rate constant was found to be about 2 × 10 9 M −1 sec −1 , decreasing slightly as the pH is increased from 5 to 9.5. A mechanism which accounts for all our observations is proposed. It includes two steps: (1) formation of a product (EO − 2 or E − ) from one enzyme (E) molecule and one O − 2 radical ion; (2) regeneration of E by a reaction of this product with an additional O − 2 ion radical. The reaction rate constants k (E+O − 2 )= (1.4 ± 0.2) × 10 9 and k (E −(or EO − 2 ) + O − 2 )= (1.9 ± 0.6) × 10 9 M −1 sec −1 were measured at pH = 7 in an oxygenated 0.16 M sodium formate solution.