Abstract
Lyophilized Escherichia coli membranes lose 50% of their DPNH oxidase activity when exposed to O 2. The oxidation of succinate or lactate is not affected by this treatment. The enzyme damaged by O 2 is the membrane DPNH dehydrogenase (DPNH-ferricyanide oxidoreductase, EC 1.6.99.3). The K m values for DPNH and the electron acceptor K 3Fe(CN) 6 are the same in the native and the inactivated enzyme. The v max of the latter is decreased by 50% for both substrates. The accessibility of non-heme iron to o-phenanthroline is partly increased. It is suggested that the non-heme iron of DPNH dehydrogenase participates in intramolecular electron conductance between the oxidizing and the reducing sites of the enzyme.
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