The Role of 4,5-Dioxovaleric Acid in Porphyrin and Vitamin B sub(12) Formation by Clostridia

4,5-Dioxovalerate, which has been proposed as an intermediate in the newly discovered so-called C sub(5) pathway that leads from L-glutamate to delta -aminolevulinate in cells of Clostridum tetanomorphum) and in cell-free extracts of this organism, in spite of the presence of L-alanine: 4,5-dioxovalerate aminotransferase. The interference by 4,5-dioxovalerate with porphyrin formation is due to strong inhibition of delta -aminolevulinate dehydratase. Since 4,5-dioxovalerate hence effectively prevents the operation of the reaction sequence form L-glutamate to prophyrin, it is concluded that 4,5-dioxovalerate does not function as a physiological delta -aminolevulinate precursor.