Regulation of 2-oxoglutarate dehydrogenase synthesis in Citrobacter freundii by traces of oxygen in commercial nitrogen gas and by glutamate.

Glutamate induced the synthesis of 2-oxoglutarate dehydrogenase 50-fold during anaerobic growth of Citrobacter freundii and, in the absence of glutamate, this enzyme was even more active in cultures sparged with N2/CO2(95:5, v/v). Enzyme synthesis was partially repressed when the inlet gas was passed through heated copper but totally repressed when the inlet gas was passed through alkaline pyrogallol and reduced benzyl viologen (a treatment which would remove CO2 as well as O2). Fumarate hydratase activity also decreased but alcohol dehydrogenase and the sum of the succinate dehydrogenase and fumarate reductase activities increased when residual O2 was removed from the sparging gas. Soluble cytochromes a1 and c552.5 were detected in rigorously anaerobic cultures. Thus traces of O2 which contaminate commercial compressed N2 are sufficient to induce 2-oxoglutarate dehydrogenase synthesis and to affect significantly the synthesis and incorporation of respiratory chain components into the cytoplasmic membrane.