Evidence for a dipyrromethane cofactor at the catalytic site of E. coli porphobilinogen deaminase

Porphobilinogen deaminase isolated from Escherichia coli is shown to contain a dipyrromethane cofactor (DPMC) linked covalently to the enzyme. The structure of the cofactor is proposed on the basis of its reaction with Ehrlich's reagent and from its chemical properties. The cofactor is involved in the binding of intermediates during the catalytic reaction but is not incorporated into the product preuroporphyrinogen, E. coli strains containing the cloned porphobilinogen deaminase gene ( hemC) when grown on 5-amino[ 14C]-levulinic acid incorporate 14C radioactivity specifically into the dipyrromethane cofactor of porphobilinogen deaminase.