Biosynthesis of the natural porphyrins: proof that hydroxymethylbilane synthase (porphobilinogen deaminase) uses a novel binding group in its catalytic action

Hydroxymethylbilane synthase builds a bilane by assembling 4 monopyrrolic units, the first of these being bound covalently to the enzyme through a group X; it is proved that X represents a unique enzymic cofactor based on a pyrromethane system.