1. Brain homogenates of mice infected with the Theiler FA strain of mouse encephalomyelitis virus show marked inhibition of glucose phosphorylation.
2. A similar effect can be obtained by incubating normal brain homogenates with small amounts of ferrous sulfate.
3. Partially purified preparations of Theiler FA virus contain iron in amounts corresponding to their inhibitory effect on brain glycolysis. The virus preparations were purified by chemical fractionation and differential centrifugation and were dialyzed against potassium cyanide or pyrophosphate and potassium chloride for several days before they were analyzed for iron content.
4. The inhibitory effect of the virus preparations and of ferrous sulfate has been shown to be dependent on a heat-labile factor present in normal brain ("inactivating factor").
5. The glycolytic activity of brain homogenates of mice infected with the Theiler FA virus can be restored by addition of a factor prepared from rabbit muscle extract. This "restoring factor" is non-dialyzable and is heat-labile. It has no hexokinase or phosphohexokinase activity. Its restoring activity is destroyed by the "inactivating factor" present in brain.