The enzymic oxidn. of isoniazid by the catalase-peroxidase of Mycobacterium tuberculosi was studied. The reaction products suggest two reaction pathways involving both electrophilic and radical species. Labeling expts. are consistent with a reaction mechanism involving the formation of an acyldiimide intermediate followed by decompn. to the corresponding aldehyde and peracid. The results suggest that isoniazid is oxidized by the catalase-peroxidase to a reactive species that may act by inactivating an essential enzyme of M. tuberculosis. [on SciFinder (R)]