EVIDENCE THAT THE PYRROMETHANE COFACTOR OF HYDROXYMETHYLBILANE SYNTHASE (PORPHOBILINOGEN DEAMINASE) IS BOUND THROUGH THE SULFUR ATOM OF A CYSTEINE RESIDUE

Hydroxymethylbilane synthase (porphobilinogen deaminase) from Eschericjia coli uses a novel pyrromethane cofactor to bind the growing pyrrolic chain for hydroxymethylbilane biosynthesis [Hart, Miller, Leeper and Battersby (1987) J. Chem. Soc. Chem. Commun. 1762-1765]. We show that this cofactor is bound to the protein through the sulphur atom of a cysteine residue.