Catalyzes the hydrolytic cleavage of the carbon-nitrogen bond in imidazolone-5-propanoate to yield N-formimidoyl-L-glutamate. It is the third step in the universal histidine degradation pathway. 4-imidazolone-5-propanoate + H2O = N-formimidoyl-L-glutamate L-histidine = NH4(+) + trans-urocanate Binds 1 zinc or iron ion per subunit. Amino-acid degradation; L-histidine degradation into L-glutamate; N-formimidoyl-L-glutamate from L-histidine: step 1/3. Amino-acid degradation; L-histidine degradation into L-glutamate; N-formimidoyl-L-glutamate from L-histidine: step 3/3. Contains an active site 4-methylidene-imidazol-5-one (MIO), which is formed autocatalytically by cyclization and dehydration of residues Ala-Ser-Gly. In the N-terminal section; belongs to the metallo-dependent hydrolases superfamily. HutI family. In the C-terminal section; belongs to the PAL/histidase family.