Regulation of Histidine Catabolism by Succinate in Pseudomonas putida

The regulation of the histidine-degrading pathway is known to involve induction and repression. Our studies have shown that succinate may control the histidine-degrading pathway by sequential negative feedback inhibition. Succinate inhibited urocanase, and urocanate in turn inhibited histidase. Crude preparations of the two enzymes were made from Pseudomonas putida grown on l -histidine. Succinate was a competitive inhibitor of urocanase ( K i , 1.8 m m ). Lactate, pyruvate, α-ketoglutarate, and glutamate did not inhibit urocanase. Urocanate inhibited histidase competitively ( K i , 0.13 m m ). A multienzyme system (histidine to glutamate), when incubated with histidine and succinate, exhibited the combined effect. Succinate caused the level of accumulated urocanate to increase and indirectly blocked histidine disappearance. Growth of cells on urocanate as a nitrogen source was inhibited by 1% succinate. Succinate may play a physiological role in the biological regulation of histidine metabolism.