Ferricyanide, an artificial electron acceptor for hepatic sulfite oxidase (EC 18.104.22.168), has been shown to cause an irreversible inactivation of the enzyme by an interaction at the molybdenum center. The one-electron transferring abilities are lost first, followed by slower parallel losses of oxidase activity and enzymic molybdenum. The rate of inactivation by ferricyanide is lower in the presence of cytochrome c or any of several anions. Accompanying the loss of one-electron transfer activities are changes in the Mo(V) electron paramagnetic resonance signal and in the visible absorption spectrum. Specific degradation of the polypeptide chain takes place subsequently, but at a much slower rate than the inactivation. These results are discussed in relation to the pathways of electron entry, transport and egress in sulfite oxidase. © 1974.
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