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In vivo metal substitution in bacteroides superoxide dismutase
The effect of various growth conditions on the type of superoxide dismutase
(SGD) formed anaerobically in three Bacteriodes species was studied. B.
fragilis, B. distasonis, and B. thetaiotaomicron were grown in ironâ restricted media
with or without manganese supplementation. Iron availability was decreased
by treatment of the media with chelex-100, a metal-chelating resin, and addition
of desferrioxamine mesylate (desferal, Ciba-Geigy), an iron chelator. Mn-containing
(MnSOD) and Fe-containing superoxide dismutase (EeSOD) activities
in cell extracts were differentiated by inhibition with azide and inactivation by
H202. The amount of Mn-containing superoxide dismutase was estimated by the
fraction of azide- and H202, -resistant activity. Cells grown in untreated media
contained approximately 90% FeSOD and 10% MnSOD. Cells grown in Fe-restricted
media supplemented with graded amounts of manganese synthesized a
progressively larger fraction of MnSOD. Hemin, added to the Fe-restricted media,
did not serve as an iron source for FeSOD formation. Superoxide dismutase specific activities varied (3-6 U/mg) in each extract but not as a function of manganese concentration.