N-formimino-L-glutamate formiminohydrolase of Aerobacter aerogenes.

N-Formimino-n-glutamate is an intermediate in the degradation of n-histidine by such different types of cells as those of animal liver (1)) Pseudomonas jluorescens (2, 3), and Aerobacter aerogenes (3). The pathway leading from histidine to formiminoglutamate is the same in all cases and comprises three steps catalyzed by distinct enzymes: L-histidine is converted to urocanate and ammonia by histidine ammonia-lyase (3-5) ; urocanate is converted to L-5-imidazolone-4-propionate by urocanase (6, 7) ; and imidazolonepropionate is converted to formiminoglutamate by imidazolonepropionate amidohydrolase (6, 8). In all cases, formiminoglutamate is further degraded to glutamate. However, the mechanism of glutamate production is different in the three cell types. In animal liver glutamate is generated by the transfer of the formimino group to tetrahydrofolic acid; further reactions enable the formyl moiety to enter the pool of single carbon compounds (9). In P. Jluorescens formiminoglutamate is first hydrolyzed to ammonia and formylglutamate which in turn is hydrolyzed to glutamate and formate (2, 3) ; the formate can serve the cell as a source of single carbon compounds (10, 11). In A. aerogenes formiminoglutamate is split into glutamate and formamide (3) ; the latter compound cannot be further metabolized and accumulates in histidinecontaining cultures (12). The present paper describes the partial purification and some of the properties of the formiminoglutamate hydrolase of A. aerogenes. This investigation was prompted by our interest in the control of the synthesis of the enzymes of histidine metabolism by induction and repression. The results of an investigation of these regulatory mechanisms are presented in the succeeding papers (13-15).